13. General-purpose I/Os (GPIO)

13.1 GPIO introduction

Each general-purpose I/O port has four 32-bit configuration registers (GPIOx_MODER, GPIOx_OTYPER, GPIOx_OSPEEDR, and GPIOx_PUPDR), two 32-bit data registers (GPIOx_IDR and GPIOx_ODR), a 16-bit reset register (GPIOx_BRR) and a 32-bit set/reset register (GPIOx_BSRR).

In addition, all GPIOs have a 32-bit locking register (GPIOx_LCKR), two 32-bit alternate function selection registers (GPIOx_AFRH and GPIOx_AFRL), and a secure configuration register (GPIOx_SECCFGR).

13.2 GPIO main features

• • Output states: push-pull or open drain + pull-up/down
• • Output data from output data register (GPIOx_ODR) or peripheral (alternate function output)
• • Speed selection for each I/O
• • Input states: floating, pull-up/down, analog
• • Input-data to input-data register (GPIOx_IDR) or peripheral (alternate function input)
• • Bit set and reset register (GPIOx_BSRR) for bitwise write access to GPIOx_ODR
• • Lock mechanism (GPIOx_LCKR) provided to freeze the I/O port configurations
• • Analog function
• • Alternate function selection registers
• • Fast toggle capable of changing every two clock cycles
• • Highly flexible pin multiplexing allows the use of I/O pins as GPIOs or as one of several peripheral functions
• • High speed at low I/O voltage operation
• • TrustZone® security support

13.3 GPIO implementation

Table 118. GPIO implementation

13.4 GPIO functional description

Subject to the specific hardware characteristics of each I/O port listed in the datasheet, each port bit of the general-purpose I/O (GPIO) ports can be configured individually by software in several modes:

• • Input floating
• • Input pull-up
• • Input pull-down
• • Analog
• • Analog pull-down
• • Output open-drain with pull-up or pull-down capability
• • Output push-pull with pull-up or pull-down capability
• • Alternate function push-pull with pull-up or pull-down capability
• • Alternate function open-drain with pull-up or pull-down capability

Each I/O port bit is freely programmable; however, the I/O port registers must be accessed as 32-bit words, half-words, or bytes. The GPIOx_BSRR and GPIOx_BRR registers allow atomic read/modify accesses to any of the GPIOx_ODR registers. In this way, there is no risk of an IRQ occurring between the read and modify access operations.

GPIO configuration is only available in Run and Stop modes, it keeps the I/O port in its defined state. In Standby mode, the GPIO configuration is lost. To keep the I/O port input definition and output levels, a GPIO standby retention can be enabled in the PWR ( Section 11.7.10: PWR Standby mode ).

Figure 42 shows the basic structures of a 3 or 5 V-tolerant GPIO (TT or FT). Table 119 gives the possible port bit configurations.

Figure 42. Structure of 3 or 5 V-tolerant GPIO (TT or FT)

1. GP = general-purpose, PP = push-pull, PU = pull-up, PD = pull-down, OD = open-drain, AF = alternate function.

13.4.1 GPIO general-purpose I/O

During and just after reset, the alternate functions are not active and most of the I/O ports are configured in analog mode.

The debug pins are in AF pull-up/pull-down after reset:

• • PA15: JTDI in pull-up
• • PA14: JTCK/SWCLK in pull-down
• • PA13: JTMS/SWDIO in pull-up
• • PB4: NJTRST in pull-up
• • PB3: JTDO/TRACEWO in floating state, no pull-up/pull-down

PH3/BOOT0 is in input mode during the reset until at least the end of the option byte loading phase (see Section 13.4.17 ).

When the pin is configured as output, the value written in the output data register (GPIOx_ODR) is output on the I/O pin. It is possible to use the output driver in push-pull mode or open-drain mode (only the low level is driven; high level is high-Z).

The input data register (GPIOx_IDR) captures the data present on the I/O pin at every AHB clock cycle.

All GPIO pins have weak internal pull-up and pull-down resistors that can be activated or deactivated depending on the value in the GPIOx_PUPDR register.

13.4.2 GPIO pin alternate function multiplexer and mapping

The device I/O pins are connected to on-board peripherals/modules through a multiplexer that allows only one peripheral alternate function (AF) connected to an I/O pin at a time. This way, there is no conflict between peripherals available on the same I/O pin.

Each I/O pin has a multiplexer with up to 16 alternate function inputs (AF0 to AF15) that can be configured through the GPIOx_AFRL (for pin 0 to 7) and GPIOx_AFRH (for pin 8 to 15) registers:

• • After reset, the multiplexer selection is alternate function 0 (AF0). The I/Os are configured in alternate function mode through the GPIOx_MODER register.
• • The specific alternate function assignments for each pin are detailed in the device datasheet.

In addition to this flexible I/O multiplexing architecture, each peripheral has alternate functions mapped onto different I/O pins to optimize the number of peripherals available in smaller packages.

For secure peripherals, the GPIO pin must also be secure to use the secure peripheral alternate function.

To use an I/O in a given configuration, the user must proceed as follows:

• • Debug function: after each device reset these pins are assigned as alternate function pins immediately usable by the debugger host.
• • GPIO: configure the desired I/O as output, input, or analog in the GPIOx_MODER register.
• • Peripheral alternate function:
  • – Connect the I/O to the desired alternate function in one of the GPIOx_AFRRL or GPIOx_AFRH register.
  • – Select the type, pull-up/pull-down, and output speed via the GPIOx_OTYPER, GPIOx_PUPDR, and GPIOx_OSPEEDER registers respectively.
  • – Configure the desired I/O as an alternate function in the GPIOx_MODER register.
• • Additional functions:
  • – For the ADC, configure the desired I/O in analog mode in the GPIOx_MODER register and configure the required function in the ADC registers.
  • – For the additional functions like RTC, TAMP, WKUP, and LSE configure the required function in the related peripheral register. These functions have priority over the configuration in the GPIO registers.

Refer to the “Alternate function mapping” table in the device datasheet for the detailed mapping of the alternate function I/O pins.

13.4.3 GPIO port control registers

Each of the GPIO ports has four 32-bit memory-mapped control registers (GPIOx_MODER, GPIOx_OTYPER, GPIOx_OSPEEDER, GPIOx_PUPDR) to configure up to 16 I/Os. The GPIOx_MODER register is used to select the I/O mode (input, output, AF, analog). The GPIOx_OTYPER and GPIOx_OSPEEDER registers are used to select the output type (push-pull or open-drain) and speed. The GPIOx_PUPDR register is used to select the pull-up/pull-down whatever the I/O direction.

13.4.4 GPIO port data registers

Each GPIO has two 16-bit memory-mapped data registers: input and output data registers ( GPIO port A input data register (GPIOA_IDR) and GPIO port A output data register (GPIOA_ODR) ).

GPIOx_ODR stores the data to be output, it is read/write accessible. The data that are input through the I/O are stored in the input data register (GPIOx_IDR), which is a read-only register.

13.4.5 GPIO data bitwise handling

The bit set reset register (GPIOx_BSRR) is a 32-bit register that allows the application to set and reset each individual bit in the output data register (GPIOx_ODR). This register is twice the size of GPIOx_ODR.

Two control bits in GPIOx_BSRR, namely BSy and BRy correspond to each bit in GPIOx_ODR. When set, BSy sets the corresponding ODRy bit. When BRy is set, it resets the corresponding ODRy bit.

Clearing a bit in GPIOx_BSRR does not affect the corresponding bit in GPIOx_ODR. If there is an attempt to set and reset a bit in GPIOx_BSRR, the set action takes priority.

Using the GPIOx_BSRR register to change the values of individual bits in GPIOx_ODR is a “one-shot” effect that does not lock the GPIOx_ODR bits. The GPIOx_ODR bits can always be accessed directly. The GPIOx_BSRR register provides a way of performing atomic bitwise handling.

There is no need for the software to disable interrupts when programming the GPIOx_ODR at bit level: one or more bits can be modified in a single atomic AHB write access.

Individual bits in GPIOx_ODR can also be reset in a single atomic AHB write to GPIOx_BRR.

13.4.6 GPIO locking mechanism

The GPIO control registers can be frozen by applying a specific write sequence to the GPIOx_LCKR register. The frozen registers are GPIOx_MODER, GPIOx_OTYPER, GPIOx_OSPEEDR, GPIOx_PUPDR, GPIOx_AFRL, and GPIOx_AFRH.

To write the GPIOx_LCKR register, a specific write/read sequence must be applied. When the right LOCK sequence is applied to bit 16 in this register, the value of LCKR[15:0] is used to lock the configuration of the I/Os (during the write sequence the LCKR[15:0] value must be the same). When the LOCK sequence is applied to a port bit, the value of the port bit can no longer be modified until the next MCU reset or peripheral reset. Each GPIOx_LCKR bit freezes the corresponding bit in the control registers (GPIOx_MODER, GPIOx_OTYPER, GPIOx_OSPEEDR, GPIOx_PUPDR, GPIOx_AFRL, and GPIOx_AFRH).

The LOCK sequence can only be performed using (32-bit) word access to the GPIOx_LCKR register because GPIOx_LCKR bit 16 must be set at the same time as bits [15:0].

13.4.7 GPIO alternate function input/output

Two registers are provided to select one of the alternate function inputs/outputs available for each I/O. With these registers, the user can connect an alternate function to some other pin as required by the application.

This means that a number of possible peripheral functions are multiplexed on each GPIO using the GPIOx_AFRL and GPIOx_AFRH alternate function registers. The application can thus select any one of the possible functions for each I/O. The AF selection signal being common to the alternate function input and alternate function output, a single channel is selected for the alternate function input/output of a given I/O.

To know which functions are multiplexed on each GPIO pin, refer to the device datasheet.

13.4.8 GPIO external interrupt/wake-up lines

All ports have external interrupt capability. To use external interrupt lines, the port can be configured in input, output, or alternate function mode (the port must not be configured in analog mode). Refer to Section 18: Extended interrupts and event controller (EXTI) .

13.4.9 GPIO input configuration

When the I/O port is programmed as input:

• • The output buffer is disabled.
• • The Schmitt trigger input is activated.
• • The pull-up and pull-down resistors are activated depending on the value in the GPIOx_PUPDR register.
• • The data present on the I/O pin are sampled into the input data register every AHB clock cycle.
• • Read access to the input data register provides the I/O state.

Figure 43 shows the input configuration of the I/O port bit.

13.4.10 GPIO output configuration

When the I/O port is programmed as output:

• • The output buffer is enabled:
  • – Open-drain mode: a 0 in the output register activates the N-MOS, whereas a 1 in the output register leaves the port in high-Z (the P-MOS is never activated).
  • – Push-pull mode: a 0 in the output register activates the N-MOS whereas a 1 in the output register activates the P-MOS.
• • The Schmitt trigger input is activated.
• • The pull-up and pull-down resistors are activated depending on the value in the GPIOx_PUPDR register.
• • The data present on the I/O pin are sampled into the input data register every AHB clock cycle.
• • Read access to the input data register gets the I/O state.
• • Read access to the output data register gets the last written value.

Figure 44 shows the output configuration of the I/O port bit.

Figure 44. Output configuration

13.4.11 GPIO alternate function configuration

When the I/O port is programmed as alternate function:

• • The output buffer can be configured in open-drain or push-pull mode.
• • The output buffer is driven by the signals coming from the peripheral (transmitter enable and data).
• • The Schmitt trigger input is activated.
• • The weak pull-up and pull-down resistors are activated or not depending on the value in the GPIOx_PUPDR register.
• • The data present on the I/O pin are sampled into the input data register every AHB clock cycle.
• • Read access to the input data register gets the I/O state.

Figure 45 shows the alternate function configuration of the I/O port bit.

Figure 45. Alternate function configuration

13.4.12 GPIO analog configuration

When the I/O port is programmed as analog configuration:

• • The output buffer is disabled.
• • The Schmitt trigger input is deactivated, providing zero consumption for every analog value of the I/O pin. The output of the Schmitt trigger is forced to a constant value (0).
• • The weak pull-down resistor is activated depending on the value in the GPIOx_PUPDR register. The weak pull-up resistor is disabled by hardware.
• • Read access to the input data register gets the value 0.

Figure 46 shows the high-Z, analog-input configuration of the I/O port bits.

graph LR
    subgraph "Internal Circuitry"
        IDR[Input data register]
        ODR[Output data register]
        BSRR[Bit set/reset registers]
        ST[TTL Schmitt trigger - OFF]
        ID[Input driver - OFF]
        OD[Output driver - OFF]
    end
    Pin((I/O pin)) --- PD[Protection diode]
    Pin --- ESD[ESD protection]
    Pin --- PDR[Pull down resistor]
    Pin --- Analog[Analog to peripheral]
    Pin --- ST
    ST --- IDR
    ODR --- OD
    BSRR --- ODR
    PD --- Vss
    ESD --- Vss
    PDR --- Vss
  

13.4.13 GPIO compensation cell

The I/O commutation slew rate ( \( t_{fall}/t_{rise} \) ) can be adapted by software depending on process, voltage and temperatures conditions, to reduce the I/O noise on the power supply. Refer to Section 14: System configuration controller (SYSCFG) for more details.

13.4.14 GPIO Standby retention

The I/O state can be retained in Standby mode. This is configured in the PWR.

13.4.15 GPIO using the LSE oscillator pins as GPIOs

When the LSE oscillator is switched off (default state after reset), the related oscillator pins can be used as normal GPIOs.

When the LSE oscillator is switched on (by setting the LSEON bit in the RCC_BDCR register), the oscillator takes control of its associated pins and the GPIO configuration of these pins has no effect.

When the oscillator is configured in a user external clock mode, only the pin is reserved for clock input, and the OSC32_OUT pin can still be used as normal GPIO.

13.4.16 GPIO using GPIO pins with RTC

The PC13/PC14/PC15 GPIO functionality is lost when the Core domain is powered off (when the device enters Standby mode). In this case, if their GPIO configuration is not

bypassed by the RTC configuration, these pins are, when not retained in Standby mode, set in analog input mode.

For details about I/O control by the RTC, refer to Section 33.3: RTC functional description .

13.4.17 GPIO using PH3 as GPIO

PH3 may be used as boot pin (BOOT0) or as a GPIO. Depending on the nSWBOOT0 user option bit in the FLASH_OPTR register, PH3 switches from input mode to analog input mode. This happens:

• • After the option byte loading phase if nSWBOOT0 = 1
• • After reset if nSWBOOT0 = 0

13.4.18 GPIO TrustZone ^® security

The TrustZone ^® security is activated by the TZEN user option bit in the FLASH_OPTR register. When TrustZone ^® is enabled (TZEN = 1), each I/O pin of the GPIO port can be individually configured as secure through the GPIOx_SECCFGR register.

When the selected I/O pin is configured as secure, its corresponding configuration bits for alternate function, mode selection, and I/O data are secured from nonsecure access operations. In the case of a nonsecure access operation, these bits are RAZ/WI.

The I/Os with peripheral functions are also conditioned by the peripheral security configuration (see Section 5: Global TrustZone ^® controller (GTZC) for more details):

• • For peripherals for which the I/O pin selection is done through alternate function registers: if the peripheral is configured as secure, it cannot be connected to a nonsecure I/O pin. If this is not respected, the input data to the secure peripheral is forced to 0 (the I/O input pin value is ignored) and the output pin value is forced to 0, thus avoiding any secure information leaks through nonsecure I/Os.
• • For I/Os with analog switches, directly controlled by peripherals (such as ADC): if the I/O is secure, the I/O analog switch cannot be controlled by a nonsecure peripheral. If this is not respected, the switch remains open. This prevents the redirection of secure data to a nonsecure peripheral or I/O through analog path. Refer to Section 4: System security for more details.
• • Some of the paths between I/O “additional functions” and peripherals are not blocked if the I/O is secure and the peripheral is nonsecure. Therefore, it is recommended that those peripherals be configured as secure even when not used by the application. Refer to Section 4: System security for the list of concerned peripherals. When the path has a security control, it follows the same rule as I/O selection through alternate functions.

Refer to the device pins definition table in the datasheet for more information about peripheral alternate functions and additional function mapping.

After reset, all GPIO ports are secure.

Table 120 gives a summary of the I/O port secured bits following the security configuration bit in the GPIOx_SECCFGR register. When the I/O bit port is configured as secure:

• Secured bits: read and write operations are only allowed by secure access. Nonsecure read or write access operations on secured bits are RAZ/WI. No illegal access event is generated.
• Nonsecure bits: no restriction. Read and write operations are allowed by both secure and nonsecure access operations.

When TrustZone® security is disabled (TZEN = 0), all registers bits are nonsecure. The GPIOx_SECCFGR register is RAZ/WI.

Table 120. GPIO secured bits

1. x = port index, y = port pin index, for values see Table 118: GPIO implementation .

As soon as at least one function is configured as secure, the GPIO reset and clock control bits in the RCC are also secured.

13.4.19 GPIO privileged and unprivileged modes

All GPIO registers can be read and written by privileged and unprivileged access, whatever the security state (secure or nonsecure).

13.5 GPIO port A registers

This section gives a detailed description of the GPIO port A registers.

The peripheral registers can be written in word, half-word, or byte mode.

13.5.1 GPIO port A mode register (GPIOA_MODER)

Address offset: 0x000

Reset value: 0xABFF FC3F

Bits 31:30 MODE15[1:0] : Port configuration I/O pin 15

These bits are written by software to configure the I/O mode.

Access can be protected by GPIOA_SEC15.

00: Input mode

01: General purpose output mode

10: Alternate function mode

11: Analog mode (reset state)

Bits 29:28 MODE14[1:0] : Port configuration I/O pin 14

Bits 27:26 MODE13[1:0] : Port configuration I/O pin 13

Bits 25:24 MODE12[1:0] : Port configuration I/O pin 12

Bits 23:22 MODE11[1:0] : Port configuration I/O pin 11

Bits 21:20 MODE10[1:0] : Port configuration I/O pin 10

Bits 19:18 MODE9[1:0] : Port configuration I/O pin 9

Bits 17:16 MODE8[1:0] : Port configuration I/O pin 8

Bits 15:14 MODE7[1:0] : Port configuration I/O pin 7

Bits 13:12 MODE6[1:0] : Port configuration I/O pin 6

Bits 11:10 MODE5[1:0] : Port configuration I/O pin 5

Bits 9:6 Reserved, must be kept at reset value.

Bits 5:4 MODE2[1:0] : Port configuration I/O pin 2

Bits 3:2 MODE1[1:0] : Port configuration I/O pin 1

Bits 1:0 MODE0[1:0] : Port configuration I/O pin 0

13.5.2 GPIO port A output type register (GPIOA_OTYPER)

Address offset: 0x004

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

These bits are written by software to configure the I/O output type.

Access can be protected by GPIOA SECy.

0: Output push-pull (reset state)

1: Output open-drain

Bits 4:3 Reserved, must be kept at reset value.

13.5.3 GPIO port A output speed register (GPIOA_OSPEEDR)

Address offset: 0x008

Reset value: 0x0800 0000

These bits are written by software to configure the I/O output speed.

Access can be protected by GPIOA SEC15.

00: Low speed

01: Medium speed

10: High speed

11: Reserved

Bits 21:20 OSPEED10[1:0] : Port configuration I/O pin 10
Bits 19:18 OSPEED9[1:0] : Port configuration I/O pin 9
Bits 17:16 OSPEED8[1:0] : Port configuration I/O pin 8
Bits 15:14 OSPEED7[1:0] : Port configuration I/O pin 7
Bits 13:12 OSPEED6[1:0] : Port configuration I/O pin 6
Bits 11:10 OSPEED5[1:0] : Port configuration I/O pin 5
Bits 9:6 Reserved, must be kept at reset value.
Bits 5:4 OSPEED2[1:0] : Port configuration I/O pin 2
Bits 3:2 OSPEED1[1:0] : Port configuration I/O pin 1
Bits 1:0 OSPEED0[1:0] : Port configuration I/O pin 0

13.5.4 GPIO port A pull-up/pull-down register (GPIOA_PUPDR)

Address offset: 0x00C

Reset value: 0x6400 0000

Bits 31:30 PUPD15[1:0] : Port configuration I/O pin 15
These bits are written by software to configure the I/O pull-up or pull-down.
Access can be protected by GPIOA SEC15.
00: No pull-up, pull-down
01: Pull-up
10: Pull-down
11: Reserved

Bits 29:28 PUPD14[1:0] : Port configuration I/O pin 14
Bits 27:26 PUPD13[1:0] : Port configuration I/O pin 13
Bits 25:24 PUPD12[1:0] : Port configuration I/O pin 12
Bits 23:22 PUPD11[1:0] : Port configuration I/O pin 11
Bits 21:20 PUPD10[1:0] : Port configuration I/O pin 10
Bits 19:18 PUPD9[1:0] : Port configuration I/O pin 9
Bits 17:16 PUPD8[1:0] : Port configuration I/O pin 8
Bits 15:14 PUPD7[1:0] : Port configuration I/O pin 7
Bits 13:12 PUPD6[1:0] : Port configuration I/O pin 6
Bits 11:10 PUPD5[1:0] : Port configuration I/O pin 5
Bits 9:6 Reserved, must be kept at reset value.

Bits 5:4 PUPD2[1:0] : Port configuration I/O pin 2

Bits 3:2 PUPD1[1:0] : Port configuration I/O pin 1

Bits 1:0 PUPD0[1:0] : Port configuration I/O pin 0

13.5.5 GPIO port A input data register (GPIOA_IDR)

Address offset: 0x010

Reset value: 0x0000 XXXX

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:5 ID[15:5] : Port input data I/O pin y (y = 15 to 5)

These bits are read-only. They contain the input value of the corresponding I/O port.

Access can be protected by GPIOA SECy.

Bits 4:3 Reserved, must be kept at reset value.

Bits 2:0 ID[2:0] : Port input data I/O pin y (y = 2 to 0)

13.5.6 GPIO port A output data register (GPIOA_ODR)

Address offset: 0x014

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:5 OD[15:5] : Port output data I/O pin y (y = 15 to 5)

These bits can be read and written by software.

Access can be protected by GPIOA SECy.

Note: For atomic bit set/reset, the OD bits can be individually set and/or reset by writing to the GPIOA_BSRR or GPIOA_BRR registers.

Bits 4:3 Reserved, must be kept at reset value.

Bits 2:0 OD[2:0] : Port output data I/O pin y (y = 2 to 0)

13.5.7 GPIO port A bit set/reset register (GPIOA_BSRR)

Address offset: 0x018

Reset value: 0x0000 0000

Bits 31:21 BR[15:5] : Port reset I/O pin y (y = 15 to 5)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOA SECy.

0: No action on the corresponding ODy bit

1: Resets the corresponding ODy bit

Note: If both BSy and BRy are set, BSy has priority.

Bits 20:19 Reserved, must be kept at reset value.

Bits 18:16 BR[2:0] : Port reset I/O pin y (y = 2 to 0)

Bits 15:5 BS[15:5] : Port set I/O pin y (y = 15 to 5)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOA SECy.

0: No action on the corresponding ODy bit

1: Sets the corresponding ODy bit

Bits 4:3 Reserved, must be kept at reset value.

Bits 2:0 BS[2:0] : Port set I/O pin y (y = 2 to 0)

13.5.8 GPIO port A configuration lock register (GPIOA_LCKR)

Address offset: 0x01C

Reset value: 0x0000 0000

This register is used to lock the configuration of the port bits when a correct write sequence is applied to bit 16 (LCKK). The value of bits [15:0] is used to lock the configuration of the GPIO. During the write sequence, the value of LCKR[15:0] must not change. When the LOCK sequence has been applied on a port bit, the value of this port bit can no longer be modified until the next MCU reset or peripheral reset.

Note: A specific write sequence is used to write to the GPIOA_LCKR register. Only (32-bit) word access is allowed during this locking sequence.

Each lock bit freezes a specific configuration register (control and alternate function registers).

Bits 31:17 Reserved, must be kept at reset value.

Bit 16 LCKK : Lock key

This bit can be read any time. It can only be modified using the lock key write sequence.

Access can be protected by any GPIOA SECy.

0: Port configuration lock key not active

1: Port configuration lock key active. The GPIOx_LCKR register is locked until the next MCU reset or peripheral reset.

- LOCK key write sequence:

WR LCKR[16] = 1 + LCKR[15:0]
WR LCKR[16] = 0 + LCKR[15:0]
WR LCKR[16] = 1 + LCKR[15:0]

- LOCK key read

RD LCKR[16] = 1 (this read operation is optional but it confirms that the lock is active)

Note: During the LOCK key write sequence, the value of LCKR[15:0] must not change.

Any error in the lock sequence aborts the LOCK.

After the first LOCK sequence on any bit of the port, any read access on the LCKK bit returns 1 until the next MCU reset or peripheral reset.

Bits 15:5 LCK[15:5] : Port lock I/O pin y (y = 15 to 5)

These bits are read/write but can only be written when the LCKK bit is 0

Access can be protected by GPIOA SECy.

0: Port configuration not locked

1: Port configuration locked

Bits 4:3 Reserved, must be kept at reset value.

Bits 2:0 LCK[2:0] : Port lock I/O pin y (y = 2 to 0)

13.5.9 GPIO port A alternate function low register (GPIOA_AFRL)

Address offset: 0x020

Reset value: 0x0000 0000

Bits 31:28 AFSEL7[3:0] : Alternate function selection for port I/O pin 7

These bits are written by software to configure alternate function I/Os.
Access can be protected by GPIOA SEC7.

0000: AF0
0001: AF1
0010: AF2
0011: AF3
0100: AF4
0101: AF5
0110: AF6
0111: AF7
1000: AF8
1001: AF9
1010: AF10
1011: AF11
1100: AF12
1101: AF13
1110: AF14
1111: AF15

Bits 27:24 AFSEL6[3:0] : Alternate function selection for port I/O pin 6

Bits 23:20 AFSEL5[3:0] : Alternate function selection for port I/O pin 5

Bits 19:12 Reserved, must be kept at reset value.

Bits 11:8 AFSEL2[3:0] : Alternate function selection for port I/O pin 2

Bits 7:4 AFSEL1[3:0] : Alternate function selection for port I/O pin 1

Bits 3:0 AFSEL0[3:0] : Alternate function selection for port I/O pin 0

13.5.10 GPIO port A alternate function high register (GPIOA_AFRH)

Address offset: 0x024

Reset value: 0x0000 0000

Bits 31:28 AFSEL15[3:0] : Alternate function selection for port I/O pin 15

These bits are written by software to configure alternate function I/Os.

Access can be protected by GPIOA SEC15.

0000: AF0

0001: AF1

0010: AF2

0011: AF3

0100: AF4

0101: AF5

0110: AF6

0111: AF7

1000: AF8

1001: AF9

1010: AF10

1011: AF11

1100: AF12

1101: AF13

1110: AF14

1111: AF15

Bits 27:24 AFSEL14[3:0] : Alternate function selection for port I/O pin 14

Bits 23:20 AFSEL13[3:0] : Alternate function selection for port I/O pin 13

Bits 19:16 AFSEL12[3:0] : Alternate function selection for port I/O pin 12

Bits 15:12 AFSEL11[3:0] : Alternate function selection for port I/O pin 11

Bits 11:8 AFSEL10[3:0] : Alternate function selection for port I/O pin 10

Bits 7:4 AFSEL9[3:0] : Alternate function selection for port I/O pin 9

Bits 3:0 AFSEL8[3:0] : Alternate function selection for port I/O pin 8

13.5.11 GPIO port A bit reset register (GPIOA_BRR)

Address offset: 0x028

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:5 BR[15:5] : Port reset I/O pin y (y = 15 to 5)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOA SECy.

0: No action on the corresponding ODy bit

1: Reset the corresponding ODy bit

Bits 4:3 Reserved, must be kept at reset value.

Bits 2:0 BR[2:0] : Port reset I/O pin y (y = 2 to 0)

13.5.12 GPIO port A secure configuration register (GPIOA_SECCFGR)

Address offset: 0x030

Reset value: 0x0000 FFFF

When the system is secure (TZEN = 1), this register provides write access security and can be written only by a secure access operation. It is used to configure a selected I/O as secure. A nonsecure write access operation to this register is discarded.

When the system is not secure (TZEN = 0), this register is RAZ/WI.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:5 SEC[15:5] : I/O pin of port secure bit enable y (y = 15 to 5)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bits 4:3 Reserved, must be kept at reset value.

Bits 2:0 SEC[2:0] : I/O pin of port secure bit enable y (y = 2 to 0)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

13.6 GPIO port B registers

This section gives a detailed description of the GPIO port B registers.

The peripheral registers can be written in word, half-word, or byte mode.

13.6.1 GPIO port B mode register (GPIOB_MODER)

Address offset: 0x000

Reset value: 0xC30F 3EB0

Bits 31:30 MODE15[1:0] : Port configuration I/O pin 15

These bits are written by software to configure the I/O mode.

Access can be protected by GPIOB SEC15.

00: Input mode

01: General purpose output mode

10: Alternate function mode

11: Analog mode (reset state)

Bits 29:26 Reserved, must be kept at reset value.

Bits 25:24 MODE12[1:0] : Port configuration I/O pin 12

Bits 23:20 Reserved, must be kept at reset value.

Bits 19:18 MODE9[1:0] : Port configuration I/O pin 9

Bits 17:16 MODE8[1:0] : Port configuration I/O pin 8

Bits 15:14 Reserved, must be kept at reset value.

Bits 13:12 MODE6[1:0] : Port configuration I/O pin 6

Bits 11:10 MODE5[1:0] : Port configuration I/O pin 5

Bits 9:8 MODE4[1:0] : Port configuration I/O pin 4

Bits 7:6 MODE3[1:0] : Port configuration I/O pin 3

Bits 5:4 MODE2[1:0] : Port configuration I/O pin 2

Bits 3:0 Reserved, must be kept at reset value.

13.6.2 GPIO port B output type register (GPIOB_OTYPER)

Address offset: 0x004

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bit 15 OT[15] : Port configuration I/O pin y (y = 15)

These bits are written by software to configure the I/O output type.

Access can be protected by GPIOB SEC15.

0: Output push-pull (reset state)

1: Output open-drain

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 OT[12] : Port configuration I/O pin y (y = 12)

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 OT[9:8] : Port configuration I/O pin y (y = 9 to 8)

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 OT[6:2] : Port configuration I/O pin y (y = 6 to 2)

Bits 1:0 Reserved, must be kept at reset value.

13.6.3 GPIO port B output speed register (GPIOB_OSPEEDR)

Address offset: 0x008

Reset value: 0x0000 0080

Bits 31:30 OSPEED15[1:0] : Port configuration I/O pin 15

These bits are written by software to configure the I/O output speed.

Access can be protected by GPIOB SEC15.

00: Low speed

01: Medium speed

10: High speed

11: Reserved

Note: Refer to the device datasheet for the frequency specifications and the power supply and load conditions for each speed.

Bits 29:26 Reserved, must be kept at reset value.

Bits 25:24 OSPEED12[1:0] : Port configuration I/O pin 12

Bits 23:20 Reserved, must be kept at reset value.

Bits 19:18 OSPEED9[1:0] : Port configuration I/O pin 9

Bits 17:16 OSPEED8[1:0] : Port configuration I/O pin 8

Bits 15:14 Reserved, must be kept at reset value.

Bits 13:12 OSPEED6[1:0] : Port configuration I/O pin 6

Bits 11:10 OSPEED5[1:0] : Port configuration I/O pin 5

Bits 9:8 OSPEED4[1:0] : Port configuration I/O pin 4

Bits 7:6 OSPEED3[1:0] : Port configuration I/O pin 3

Bits 5:4 OSPEED2[1:0] : Port configuration I/O pin 2

Bits 3:0 Reserved, must be kept at reset value.

13.6.4 GPIO port B pull-up/pull-down register (GPIOB_PUPDR)

Address offset: 0x00C

Reset value: 0x0000 0100

These bits are written by software to configure the I/O pull-up or pull-down.

Access can be protected by GPIOB SEC15.

00: No pull-up, pull-down

01: Pull-up

10: Pull-down

11: Reserved

Bits 29:26 Reserved, must be kept at reset value.

Bits 23:20 Reserved, must be kept at reset value.

Bits 15:14 Reserved, must be kept at reset value.

Bits 3:0 Reserved, must be kept at reset value.

13.6.5 GPIO port B input data register (GPIOB_IDR)

Address offset: 0x010

Reset value: 0x0000 XXXX

Bits 31:16 Reserved, must be kept at reset value.

Bit 15 ID[15] : Port input data I/O pin y (y = 15)

These bits are read-only. They contain the input value of the corresponding I/O port.

Access can be protected by GPIOB SECy.

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 ID[12] : Port input data I/O pin y (y = 12)

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 ID[9:8] : Port input data I/O pin y (y = 9 to 8)

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 ID[6:2] : Port input data I/O pin y (y = 6 to 2)

Bits 1:0 Reserved, must be kept at reset value.

13.6.6 GPIO port B output data register (GPIOB_ODR)

Address offset: 0x014

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bit 15 OD[15] : Port output data I/O pin y (y = 15)

These bits can be read and written by software.

Access can be protected by GPIOB SECy.

Note: For atomic bit set/reset, the OD bits can be individually set and/or reset by writing to the GPIOB_BSRR or GPIOB_BRR registers.

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 OD[12] : Port output data I/O pin y (y = 12)

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 OD[9:8] : Port output data I/O pin y (y = 9 to 8)

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 OD[6:2] : Port output data I/O pin y (y = 6 to 2)

Bits 1:0 Reserved, must be kept at reset value.

13.6.7 GPIO port B bit set/reset register (GPIOB_BSRR)

Address offset: 0x018

Reset value: 0x0000 0000

Bit 31 BR[15] : Port reset I/O pin y (y = 15)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOB SECy.

0: No action on the corresponding ODy bit

1: Resets the corresponding ODy bit

If both BSy and BRy are set, BSy has priority.

Bits 30:29 Reserved, must be kept at reset value.

Bit 28 BR[12] : Port reset I/O pin y (y = 12)

Bits 27:26 Reserved, must be kept at reset value.

Bits 25:24 BR[9:8] : Port reset I/O pin y (y = 9 to 8)

Bit 23 Reserved, must be kept at reset value.

Bits 22:18 BR[6:2] : Port reset I/O pin y (y = 6 to 2)

Bits 17:16 Reserved, must be kept at reset value.

Bit 15 BS[15] : Port set I/O pin y (y = 15)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOB SECy.

0: No action on the corresponding ODy bit

1: Sets the corresponding ODy bit

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 BS[12] : Port set I/O pin y (y = 12)

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 BS[9:8] : Port set I/O pin y (y = 9 to 8)

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 BS[6:2] : Port set I/O pin y (y = 6 to 2)

Bits 1:0 Reserved, must be kept at reset value.

13.6.8 GPIO port B configuration lock register (GPIOB_LCKR)

Address offset: 0x01C

Reset value: 0x0000 0000

This register is used to lock the configuration of the port bits when a correct write sequence is applied to bit 16 (LCKK). The value of bits [15:0] is used to lock the configuration of the

GPIO. During the write sequence, the value of LCKR[15:0] must not change. When the LOCK sequence has been applied on a port bit, the value of this port bit can no longer be modified until the next MCU reset or peripheral reset.

Note: A specific write sequence is used to write to the GPIOB_LCKR register. Only (32-bit) word access is allowed during this locking sequence.

Each lock bit freezes a specific configuration register (control and alternate function registers).

Bits 31:17 Reserved, must be kept at reset value.

Bit 16 LCKK : Lock key

This bit can be read any time. It can only be modified using the lock key write sequence.

Access can be protected by any GPIOB SECy.

0: Port configuration lock key not active

1: Port configuration lock key active. The GPIOx_LCKR register is locked until the next MCU reset or peripheral reset.

- LOCK key write sequence:

WR LCKR[16] = 1 + LCKR[15:0]

WR LCKR[16] = 0 + LCKR[15:0]

WR LCKR[16] = 1 + LCKR[15:0]

- LOCK key read

RD LCKR[16] = 1 (this read operation is optional but it confirms that the lock is active)

Note: During the LOCK key write sequence, the value of LCKR[15:0] must not change.

Any error in the lock sequence aborts the LOCK.

After the first LOCK sequence on any bit of the port, any read access on the LCKK bit returns 1 until the next MCU reset or peripheral reset.

Bit 15 LCK[15] : Port lock I/O pin y (y = 15)

These bits are read/write but can only be written when the LCKK bit is 0.

Access can be protected by GPIOB SECy.

0: Port configuration not locked

1: Port configuration locked

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 LCK[12] : Port lock I/O pin y (y = 12)

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 LCK[9:8] : Port lock I/O pin y (y = 9 to 8)

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 LCK[6:2] : Port lock I/O pin y (y = 6 to 2)

Bits 1:0 Reserved, must be kept at reset value.

13.6.9 GPIO port B alternate function low register (GPIOB_AFRL)

Address offset: 0x020

Reset value: 0x0000 0000

Bits 31:28 Reserved, must be kept at reset value.

Bits 27:24 AFSEL6[3:0] : Alternate function selection for port I/O pin 6

These bits are written by software to configure alternate function I/Os.

Access can be protected by GPIOB SEC6.

0000: AF0

0001: AF1

0010: AF2

0011: AF3

0100: AF4

0101: AF5

0110: AF6

0111: AF7

1000: AF8

1001: AF9

1010: AF10

1011: AF11

1100: AF12

1101: AF13

1110: AF14

1111: AF15

Bits 23:20 AFSEL5[3:0] : Alternate function selection for port I/O pin 5

Bits 19:16 AFSEL4[3:0] : Alternate function selection for port I/O pin 4

Bits 15:12 AFSEL3[3:0] : Alternate function selection for port I/O pin 3

Bits 11:8 AFSEL2[3:0] : Alternate function selection for port I/O pin 2

Bits 7:0 Reserved, must be kept at reset value.

13.6.10 GPIO port B alternate function high register (GPIOB_AFRH)

Address offset: 0x024

Reset value: 0x0000 0000

Bits 31:28 AFSEL15[3:0] : Alternate function selection for port I/O pin 15

These bits are written by software to configure alternate function I/Os.

Access can be protected by GPIOB SEC15.

0000: AF0

0001: AF1

0010: AF2

0011: AF3

0100: AF4

0101: AF5

0110: AF6

0111: AF7

1000: AF8

1001: AF9

1010: AF10

1011: AF11

1100: AF12

1101: AF13

1110: AF14

1111: AF15

Bits 27:20 Reserved, must be kept at reset value.

Bits 19:16 AFSEL12[3:0] : Alternate function selection for port I/O pin 12

Bits 15:8 Reserved, must be kept at reset value.

Bits 7:4 AFSEL9[3:0] : Alternate function selection for port I/O pin 9

Bits 3:0 AFSEL8[3:0] : Alternate function selection for port I/O pin 8

13.6.11 GPIO port B bit reset register (GPIOB_BRR)

Address offset: 0x028

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bit 15 BR[15] : Port reset I/O pin y (y = 15)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOB SECy.

0: No action on the corresponding ODy bit

1: Reset the corresponding ODy bit

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 BR[12] : Port reset I/O pin y (y = 12)

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 BR[9:8] : Port reset I/O pin y (y = 9 to 8)

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 BR[6:2] : Port reset I/O pin y (y = 6 to 2)

Bits 1:0 Reserved, must be kept at reset value.

13.6.12 GPIO port B secure configuration register (GPIOB_SECCFGR)

Address offset: 0x030

Reset value: 0x0000 FFFF

When the system is secure (TZEN = 1), this register provides write access security and can be written only by secure access. It is used to configure a selected I/O as secure. A nonsecure write access operation to this register is discarded.

When the system is not secure (TZEN = 0), this register is RAZ/WI.

Bits 31:16 Reserved, must be kept at reset value.

Bit 15 SEC[15] : I/O pin of port secure bit enable y (y = 15)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bits 14:13 Reserved, must be kept at reset value.

Bit 12 SEC[12] : I/O pin of port secure bit enable y (y = 12)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bits 11:10 Reserved, must be kept at reset value.

Bits 9:8 SEC[9:8] : I/O pin of port secure bit enable y (y = 9 to 8)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bit 7 Reserved, must be kept at reset value.

Bits 6:2 SEC[6:2] : I/O pin of port secure bit enable y (y = 6 to 2)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bits 1:0 Reserved, must be kept at reset value.

13.7 GPIO port C registers

This section gives a detailed description of the GPIO port C registers.

The peripheral registers can be written in word, half-word, or byte mode.

13.7.1 GPIO port C mode register (GPIOC_MODER)

Address offset: 0x000

Reset value: 0xFC00 0000

Bits 31:30 MODE15[1:0] : Port C configuration I/O pin 15

These bits are written by software to configure the I/O mode.

Access can be protected by GPIOC SEC15.

00: Input mode

01: General purpose output mode

10: Alternate function mode

11: Analog mode (reset state)

Bits 29:28 MODE14[1:0] : Port C configuration I/O pin 14

Bits 27:26 MODE13[1:0] : Port C configuration I/O pin 13

Bits 25:0 Reserved, must be kept at reset value.

13.7.2 GPIO port C output type register (GPIOC_OTYPER)

Address offset: 0x004

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:13 OT[15:13] : Port C configuration I/O pin y (y = 15 to 13)

These bits are written by software to configure the I/O output type.

Access can be protected by GPIOC SECy.

0: Output push-pull (reset state)

1: Output open-drain

Bits 12:0 Reserved, must be kept at reset value.

13.7.3 GPIOC port output speed register (GPIOC_OSPEEDR)

Address offset: 0x008

Reset value: 0x0000 0000

Bits 31:28 Reserved, must be kept at reset value. ⁽¹⁾

Bits 27:26 OSPEED13[1:0] : Port C configuration I/O pin 13

These bits are written by software to configure the I/O output speed.

Access can be protected by GPIOC SEC15.

00: Low speed

01: Medium speed

10: High speed

11: Reserved

Note: Refer to the device datasheet for the frequency specifications and the power supply and load conditions for each speed.

Bits 25:0 Reserved, must be kept at reset value.

1. 1. PC15 and PC14 OSPEED are fixed to Low speed.

13.7.4 GPIO port C pull-up/pull-down register (GPIOC_PUPDR)

Address offset: 0x00C

Reset value: 0x0000 0000

Bits 31:30 PUPD15[1:0] : Port C configuration I/O pin 15

These bits are written by software to configure the I/O pull-up or pull-down.

Access can be protected by GPIOC SEC15.

00: No pull-up, pull-down

01: Pull-up

10: Pull-down

11: Reserved

Bits 29:28 PUPD14[1:0] : Port C configuration I/O pin 14

Bits 27:26 PUPD13[1:0] : Port C configuration I/O pin 13

Bits 25:0 Reserved, must be kept at reset value.

13.7.5 GPIO port C input data register (GPIOC_IDR)

Address offset: 0x010

Reset value: 0x0000 X000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:13 ID[15:13] : Port C input data I/O pin y (y = 15 to 13)

These bits are read-only. They contain the input value of the corresponding I/O port.

Access can be protected by GPIOC SECy.

Bits 12:0 Reserved, must be kept at reset value.

13.7.6 GPIO port C output data register (GPIOC_ODR)

Address offset: 0x014

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:13 OD[15:13] : Port C output data I/O pin y (y = 15 to 13)

These bits can be read and written by software.

Access can be protected by GPIOC SECy.

Note: For atomic bit set/reset, the OD bits can be individually set and/or reset by writing to the GPIOC_BSRR or GPIOC_BRR registers.

Bits 12:0 Reserved, must be kept at reset value.

13.7.7 GPIO port C bit set/reset register (GPIOC_BSRR)

Address offset: 0x018

Reset value: 0x0000 0000

Bits 31:29 BR[15:13] : Port C reset I/O pin y (y = 15 to 13)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOC SECy.

0: No action on the corresponding ODy bit

1: Resets the corresponding ODy bit

Note: If both BSy and BRy are set, BSy has priority.

Bits 28:16 Reserved, must be kept at reset value.

Bits 15:13 BS[15:13] : Port C set I/O pin y (y = 15 to 13)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOC SECy.

0: No action on the corresponding ODy bit

1: Sets the corresponding ODy bit

Bits 12:0 Reserved, must be kept at reset value.

13.7.8 GPIO port C configuration lock register (GPIOC_LCKR)

Address offset: 0x01C

Reset value: 0x0000 0000

This register is used to lock the configuration of the port bits when a correct write sequence is applied to bit 16 (LCKK). The value of bits [15:13] is used to lock the configuration of the GPIO. During the write sequence, the value of LCKR[15:13] must not change. When the LOCK sequence has been applied to a port bit, the value of this port bit can no longer be modified until the next MCU reset or peripheral reset.

Note: A specific write sequence is used to write to the GPIOC_LCKR register. Only (32-bit) word access is allowed during this locking sequence.

Each lock bit freezes a specific configuration register (control and alternate function registers).

Bits 31:17 Reserved, must be kept at reset value.

Bit 16 LCKK : Lock key

This bit can be read any time. It can only be modified using the lock key write sequence.

Access can be protected by any GPIOC SECy.

0: Port configuration lock key not active

1: Port configuration lock key active. The GPIOC_LCKR register is locked until the next MCU reset or peripheral reset.

- LOCK key write sequence:

WR LCKR[16] = 1 + LCKR[15:13]

WR LCKR[16] = 0 + LCKR[15:13]

WR LCKR[16] = 1 + LCKR[15:13]

- LOCK key read

RD LCKR[16] = 1 (this read operation is optional but it confirms that the lock is active)

Note: During the LOCK key write sequence, the value of LCK[15:13] must not change.

Any error in the lock sequence aborts the LOCK.

After the first LOCK sequence on any bit of the port, any read access on the LCKK bit returns 1 until the next MCU reset or peripheral reset.

Bits 15:13 LCK[15:13] : Port C lock I/O pin y (y = 15 to 13)

These bits are read/write but can only be written when the LCKK bit is 0

Access can be protected by GPIOC SECy.

0: Port configuration not locked

1: Port configuration locked

Bits 12:0 Reserved, must be kept at reset value.

13.7.9 GPIO port C alternate function high register (GPIOC_AFRH)

Address offset: 0x024

Reset value: 0x0000 0000

Bits 31:28 AFSEL15[3:0] : Alternate function selection for port C I/O pin 15

These bits are written by software to configure alternate function I/Os.

Access can be protected by GPIOC SEC15.

0000: AF0

0001: AF1

0010: AF2

0011: AF3

0100: AF4

0101: AF5

0110: AF6

0111: AF7

1000: AF8

1001: AF9

1010: AF10

1011: AF11

1100: AF12

1101: AF13

1110: AF14

1111: AF15

Bits 27:24 AFSEL14[3:0] : Alternate function selection for port C I/O pin 14

Bits 23:20 AFSEL13[3:0] : Alternate function selection for port C I/O pin 13

Bits 19:0 Reserved, must be kept at reset value.

13.7.10 GPIO port C bit reset register (GPIOC_BRR)

Address offset: 0x028

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:13 BR[15:13] : Port reset I/O pin y (y = 15 to 13)

These bits are write-only. A read to these bits returns the value 0.

Access can be protected by GPIOC SECy.

0: No action on the corresponding ODy bit

1: Reset the corresponding ODy bit

Bits 12:0 Reserved, must be kept at reset value.

13.7.11 GPIO port C secure configuration register (GPIOC_SECCFGR)

Address offset: 0x030

Reset value: 0x0000 FFFF

When the system is secure (TZEN = 1), this register provides write access security and can be written only by a secure access. It is used to configure a selected I/O as secure. A nonsecure write access operation to this register is discarded.

When the system is not secure (TZEN = 0), this register is RAZ/WI.

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:13 SEC[15:13] : I/O pin of port C secure bit enable y (y = 15 to 13)

These bits are written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bits 12:0 Reserved, must be kept at reset value.

13.8 GPIO port H registers

This section gives a detailed description of the GPIO port H registers.

The peripheral registers can be written in word, half-word, or byte mode.

13.8.1 GPIO port H mode register (GPIOH_MODER)

Address offset: 0x000

Reset value: 0x0000 00C0

Bits 31:8 Reserved, must be kept at reset value.

Bits 7:6 MODE3[1:0] : Port H configuration I/O pin 3

These bits are written by software to configure the I/O mode.

Access can be protected by GPIOH SEC3.

00: Input mode

01: General purpose output mode

10: Alternate function mode

11: Analog mode (reset state)

Bits 5:0 Reserved, must be kept at reset value.

13.8.2 GPIO port H output type register (GPIOH_OTYPER)

Address offset: 0x004

Reset value: 0x0000 0000

Bits 31:4 Reserved, must be kept at reset value.

Bit 3 OT3 : Port H configuration I/O pin 3

This bit is written by software to configure the I/O output type.

Access can be protected by GPIOH SEC3.

0: Output push-pull (reset state)

1: Output open-drain

Bits 2:0 Reserved, must be kept at reset value.

13.8.3 GPIO port H output speed register (GPIOH_OSPEEDR)

Address offset: 0x008

Reset value: 0x0000 0000

Bits 31:8 Reserved, must be kept at reset value.

Bits 7:6 OSPEED3[1:0] : Port H configuration I/O pin 3

These bits are written by software to configure the I/O output speed.

Access can be protected by GPIOH SEC3.

00: Low speed

01: Medium speed

10: High speed

11: Reserved

Note: Refer to the device datasheet for the frequency specifications and the power supply and load conditions for each speed.

Bits 5:0 Reserved, must be kept at reset value.

13.8.4 GPIO port H pull-up/pull-down register (GPIOH_PUPDR)

Address offset: 0x00C

Reset value: 0x0000 0000

Bits 31:8 Reserved, must be kept at reset value.

Bits 7:6 PUPD3[1:0] : Port H configuration I/O pin 3

These bits are written by software to configure the I/O pull-up or pull-down.

Access can be protected by GPIOH SEC3.

00: No pull-up, pull-down

01: Pull-up

10: Pull-down

11: Reserved

Bits 5:0 Reserved, must be kept at reset value.

13.8.5 GPIO port H input data register (GPIOH_IDR)

Address offset: 0x010

Reset value: 0x0000 XXXX

Bits 31:4 Reserved, must be kept at reset value.

Bit 3 ID3 : Port H input data I/O pin 3

This bit is read-only. It contains the input value of the corresponding I/O port.

Access can be protected by GPIOH SEC3.

Bits 2:0 Reserved, must be kept at reset value.

13.8.6 GPIO port H output data register (GPIOH_ODR)

Address offset: 0x014

Reset value: 0x0000 0000

Bits 31:4 Reserved, must be kept at reset value.

Bit 3 OD3 : Port H output data I/O pin 3

This bits can be read and written by software.

Access can be protected by GPIOH SEC3.

Note: For atomic bit set/reset, the OD bit can be individually set and/or reset by writing to the GPIOH_BSRR or GPIOH_BRR registers.

Bits 2:0 Reserved, must be kept at reset value.

13.8.7 GPIO port H bit set/reset register (GPIOH_BSRR)

Address offset: 0x018

Reset value: 0x0000 0000

Bits 31:20 Reserved, must be kept at reset value.

Bit 19 BR3 : Port H reset I/O pin 3

This bit is write-only. A read to this bit returns the value 0.

Access can be protected by GPIOH SEC3.

0: No action on the corresponding OD3 bit

1: Resets the corresponding OD3 bit

Note: If both BS3 and BR3 are set, BS3 has priority.

Bits 18:4 Reserved, must be kept at reset value.

Bit 3 BS3 : Port H set I/O pin 3

This bit is write-only. A read to this bit returns the value 0.

Access can be protected by GPIOH SEC3.

0: No action on the corresponding OD3 bit

1: Sets the corresponding OD3 bit

Bits 2:0 Reserved, must be kept at reset value.

13.8.8 GPIO port H configuration lock register (GPIOH_LCKR)

Address offset: 0x01C

Reset value: 0x0000 0000

This register is used to lock the configuration of the port bits when a correct write sequence is applied to bit 16 (LCKK). The value of bit [3] is used to lock the configuration of the GPIO. During the write sequence, the value of LCKR[3] must not change. When the LOCK sequence has been applied on a port bit, the value of this port bit can no longer be modified until the next MCU reset or peripheral reset.

Note: A specific write sequence is used to write to the GPIOH_LCKR register. Only word access (32-bit long) is allowed during this locking sequence.

Each lock bit freezes a specific configuration register (control and alternate function registers).

Bits 31:17 Reserved, must be kept at reset value.

Bit 16 LCKK : Lock key

This bit can be read any time. It can only be modified using the lock key write sequence.

Access can be protected by GPIOH SEC3.

0: Port configuration lock key not active

1: Port configuration lock key active. The GPIOH_LCKR register is locked until the next MCU reset or peripheral reset.

- LOCK key write sequence:

WR LCKR[16] = 1 + LCKR[3]

WR LCKR[16] = 0 + LCKR[3]

WR LCKR[16] = 1 + LCKR[3]

- LOCK key read

RD LCKR[16] = 1 (this read operation is optional but it confirms that the lock is active)

Note: During the LOCK key write sequence, the value of LCK3 must not change.

Any error in the lock sequence aborts the LOCK.

After the first LOCK sequence on any bit of the port, any read access on the LCKK bit returns 1 until the next MCU reset or peripheral reset.

Bits 15:4 Reserved, must be kept at reset value.

Bit 3 LCK3 : Port H lock I/O pin 3

This bit is read/write but can only be written when the LCKK bit is 0.

Access can be protected by GPIOH SEC3.

0: Port configuration not locked

1: Port configuration locked

Bits 2:0 Reserved, must be kept at reset value.

13.8.9 GPIO port H alternate function low register (GPIOH_AFRL)

Address offset: 0x020

Reset value: 0x0000 0000

Bits 31:16 Reserved, must be kept at reset value.

Bits 15:12 AFSEL3[3:0] : Alternate function selection for port H I/O pin 3

These bits are written by software to configure alternate function I/Os.

Access can be protected by GPIOH SEC3.

0000: AF0

0001: AF1

0010: AF2

0011: AF3

0100: AF4

0101: AF5

0110: AF6

0111: AF7

1000: AF8

1001: AF9

1010: AF10

1011: AF11

1100: AF12

1101: AF13

1110: AF14

1111: AF15

Bits 11:0 Reserved, must be kept at reset value.

13.8.10 GPIO port H bit reset register (GPIOH_BRR)

Address offset: 0x028

Reset value: 0x0000 0000

Bits 31:4 Reserved, must be kept at reset value.

Bit 3 BR3 : Port H reset I/O pin 3

This bit is write-only. A read to this bit returns the value 0.

Access can be protected by GPIOH SEC3.

0: No action on the corresponding OD3 bit

1: Reset the corresponding OD3 bit

Bits 2:0 Reserved, must be kept at reset value.

13.8.11 GPIO port H secure configuration register (GPIOH_SECCFGR)

Address offset: 0x030

Reset value: 0x0000 FFFF

When the system is secure (TZEN = 1), this register provides write access security and can be written only by a secure access. It is used to configure a selected I/O as secure. A nonsecure write access operation to this register is discarded.

When the system is not secure (TZEN = 0), this register is RAZ/WI.

Bits 31:4 Reserved, must be kept at reset value.

Bit 3 SEC3 : I/O pin of port H secure bit enable 3

This bit is written by software to enable the security I/O port pin.

0: The I/O pin is nonsecure

1: The I/O pin is secure. Refer to Table 120 for all corresponding secured bits.

Bits 2:0 Reserved, must be kept at reset value.

13.8.12 GPIOA register map

Table 121. GPIOA register map and reset values

13.8.13 GPIOB register map

Table 122. GPIOB register map and reset values

13.8.14 GPIOC register map

Table 123. GPIOC register map and reset values