23. Basic timers (TIM6/TIM7)

23.1 TIM6/TIM7 introduction

The basic timers TIM6 and TIM7 consist of a 16-bit auto-reload counter driven by a programmable prescaler.

They may be used as generic timers for time base generation but they are also specifically used to drive the digital-to-analog converter (DAC). In fact, the timers are internally connected to the DAC and are able to drive it through their trigger outputs.

The timers are completely independent, and do not share any resources.

23.2 TIM6/TIM7 main features

Basic timer (TIM6/TIM7) features include:

Figure 310. Basic timer block diagram

Figure 310. Basic timer block diagram

The block diagram illustrates the internal architecture of a basic timer (TIM6/TIM7). At the top, a 'Trigger controller' block receives an 'Internal clock (CK_INT)' from the 'TIMxCLK from RCC' input. It has a 'Control' sub-block and outputs a 'TRGO' signal 'to DAC'. Below this, a 'CNT counter' block receives a 'CK_CNT' signal from a 'PSC prescaler' block. The 'PSC prescaler' is driven by 'CK_PSC'. The 'CNT counter' is also connected to an 'Auto-reload register' block. The 'Auto-reload register' receives 'U' (Update) events and sends 'Stop, clear or up' signals to the counter. It also has 'U' (Update) and 'UI' (Update Interrupt) outputs. A legend at the bottom left explains the symbols: 'Reg' for preload registers, a single arrow for 'Event', and a double arrow for 'Interrupt & DMA output'. The diagram is labeled 'MS33142V1' in the bottom right corner.

Figure 310. Basic timer block diagram

23.3 TIM6/TIM7 functional description

23.3.1 Time-base unit

The main block of the programmable timer is a 16-bit upcounter with its related auto-reload register. The counter clock can be divided by a prescaler.

The counter, the auto-reload register and the prescaler register can be written or read by software. This is true even when the counter is running.

The time-base unit includes:

The auto-reload register is preloaded. The preload register is accessed each time an attempt is made to write or read the auto-reload register. The contents of the preload register are transferred into the shadow register permanently or at each update event UEV, depending on the auto-reload preload enable bit (ARPE) in the TIMx_CR1 register. The update event is sent when the counter reaches the overflow value and if the UDIS bit equals 0 in the TIMx_CR1 register. It can also be generated by software. The generation of the update event is described in detail for each configuration.

The counter is clocked by the prescaler output CK_CNT, which is enabled only when the counter enable bit (CEN) in the TIMx_CR1 register is set.

Note that the actual counter enable signal CNT_EN is set 1 clock cycle after CEN.

Prescaler description

The prescaler can divide the counter clock frequency by any factor between 1 and 65536. It is based on a 16-bit counter controlled through a 16-bit register (in the TIMx_PSC register). It can be changed on the fly as the TIMx_PSC control register is buffered. The new prescaler ratio is taken into account at the next update event.

Figure 311 and Figure 312 give some examples of the counter behavior when the prescaler ratio is changed on the fly.

Figure 311. Counter timing diagram with prescaler division change from 1 to 2

Figure 311: Counter timing diagram with prescaler division change from 1 to 2. The diagram shows signals: CK_PSC (clock), CEN (counter enable), Timerclock = CK_CNT, Counter register (hex values F7 to 03), Update event (UEV), Prescaler control register (0 to 1), Prescaler buffer (0 to 1), and Prescaler counter (0 to 1). A write to TIMx_PSC occurs during the cycle, but the change only takes effect at the UEV.

The diagram illustrates the timing of a prescaler update in a timer. The top signal is CK_PSC , a periodic clock. Below it is CEN (Counter Enable), which goes high to start counting. The Timerclock = CK_CNT signal is derived from CK_PSC and is active when CEN is high. The Counter register shows values F7, F8, F9, FA, FB, FC, 00, 01, 02, 03. An Update event (UEV) occurs when the counter overflows from FC to 00. The Prescaler control register is initially 0. At a point between the first and second UEV, a new value (1) is written to the register, indicated by an arrow and the text "Write a new value in TIMx_PSC". This new value is latched into the Prescaler buffer and then applied to the Prescaler counter at the next UEV. The prescaler counter shows a sequence of 0 and 1, indicating it is toggling. The bottom right corner contains the text MS31076V2.

Figure 311: Counter timing diagram with prescaler division change from 1 to 2. The diagram shows signals: CK_PSC (clock), CEN (counter enable), Timerclock = CK_CNT, Counter register (hex values F7 to 03), Update event (UEV), Prescaler control register (0 to 1), Prescaler buffer (0 to 1), and Prescaler counter (0 to 1). A write to TIMx_PSC occurs during the cycle, but the change only takes effect at the UEV.

Figure 312. Counter timing diagram with prescaler division change from 1 to 4

Figure 312: Counter timing diagram with prescaler division change from 1 to 4. Similar to Figure 311, but the prescaler control register is updated from 0 to 3. After the UEV, the prescaler counter counts from 0 to 3, and the Timerclock (CK_CNT) frequency is divided by 4 compared to CK_PSC.

The diagram illustrates the timing and state changes for a timer's prescaler and counter. The top signal, CK_PSC, is a periodic clock. The CEN signal is active-high. The Timerclock (CK_CNT) is derived from CK_PSC and is only active when CEN is high. The Counter register shows values F7, F8, F9, FA, FB, FC, followed by a rollover to 00 and then 01. The Update event (UEV) is a pulse that occurs when the counter rolls over. The Prescaler control register is initially 0. An arrow points to it with the text "Write a new value in TIMx_PSC". The register is then updated to 3. The Prescaler buffer and Prescaler counter both follow the control register value, starting at 0 and then changing to 3. The Prescaler counter counts from 0 to 3 (0, 1, 2, 3) and then rolls over to 0. The bottom right corner contains the text MS31077V2.

Figure 312: Counter timing diagram with prescaler division change from 1 to 4. Similar to Figure 311, but the prescaler control register is updated from 0 to 3. After the UEV, the prescaler counter counts from 0 to 3, and the Timerclock (CK_CNT) frequency is divided by 4 compared to CK_PSC.

23.3.2 Counting mode

The counter counts from 0 to the auto-reload value (contents of the TIMx_ARR register), then restarts from 0 and generates a counter overflow event.

An update event can be generated at each counter overflow or by setting the UG bit in the TIMx_EGR register (by software or by using the slave mode controller).

The UEV event can be disabled by software by setting the UDIS bit in the TIMx_CR1 register. This avoids updating the shadow registers while writing new values into the preload registers. In this way, no update event occurs until the UDIS bit has been written to 0, however, the counter and the prescaler counter both restart from 0 (but the prescale rate does not change). In addition, if the URS (update request selection) bit in the TIMx_CR1 register is set, setting the UG bit generates an update event UEV, but the UIF flag is not set (so no interrupt or DMA request is sent).

When an update event occurs, all the registers are updated and the update flag (UIF bit in the TIMx_SR register) is set (depending on the URS bit):

The following figures show some examples of the counter behavior for different clock frequencies when TIMx_ARR = 0x36.

Figure 313. Counter timing diagram, internal clock divided by 1

Timing diagram for a counter in counting mode. The diagram shows the relationship between the prescaler clock (CK_PSC), counter enable (CNT_EN), timer clock (Timerclock = CK_CNT), counter register values, counter overflow, update event (UEV), and update interrupt flag (UIF).

The timing diagram illustrates the counter's behavior over time. The top signal, CK_PSC, is a periodic square wave. Below it, CNT_EN is a signal that goes high to enable the counter. When CNT_EN is high, the Timerclock = CK_CNT signal is active. The Counter register shows a sequence of values: 31, 32, 33, 34, 35, 36, 00, 01, 02, 03, 04, 05, 06, 07. The Counter overflow signal is a pulse that occurs when the counter reaches 36 and resets to 00. The Update event (UEV) signal is a pulse that occurs at the same time as the counter overflow. The Update interrupt flag (UIF) is a pulse that occurs at the same time as the counter overflow. Vertical dashed lines indicate the timing relationships between the signals.

MS31078V2

Timing diagram for a counter in counting mode. The diagram shows the relationship between the prescaler clock (CK_PSC), counter enable (CNT_EN), timer clock (Timerclock = CK_CNT), counter register values, counter overflow, update event (UEV), and update interrupt flag (UIF).

Figure 314. Counter timing diagram, internal clock divided by 2

Timing diagram for internal clock divided by 2. It shows the relationship between CK_PSC, CNT_EN, Timerclock (CK_CNT), Counter register values (0034 to 0003), Counter overflow, Update event (UEV), and Update interrupt flag (UIF).

This timing diagram illustrates the operation of a counter with an internal clock divided by 2. The signals shown are:

Vertical dashed lines indicate the timing relationships between the clock edges and the counter value changes. The diagram is labeled MS31079V2 in the bottom right corner.

Timing diagram for internal clock divided by 2. It shows the relationship between CK_PSC, CNT_EN, Timerclock (CK_CNT), Counter register values (0034 to 0003), Counter overflow, Update event (UEV), and Update interrupt flag (UIF).

Figure 315. Counter timing diagram, internal clock divided by 4

Timing diagram for internal clock divided by 4. It shows the relationship between CK_PSC, CNT_EN, Timerclock (CK_CNT), Counter register values (0035 to 0001), Counter overflow, Update event (UEV), and Update interrupt flag (UIF).

This timing diagram illustrates the operation of a counter with an internal clock divided by 4. The signals shown are:

Vertical dashed lines indicate the timing relationships between the clock edges and the counter value changes. The diagram is labeled MS31080V2 in the bottom right corner.

Timing diagram for internal clock divided by 4. It shows the relationship between CK_PSC, CNT_EN, Timerclock (CK_CNT), Counter register values (0035 to 0001), Counter overflow, Update event (UEV), and Update interrupt flag (UIF).

Figure 316. Counter timing diagram, internal clock divided by N

Timing diagram for Figure 316 showing counter behavior with internal clock divided by N.

This timing diagram illustrates the operation of a counter when the internal clock is divided by N. The signals shown are:

MS31081V2

Timing diagram for Figure 316 showing counter behavior with internal clock divided by N.

Figure 317. Counter timing diagram, update event when ARPE = 0 (TIMx_ARR not preloaded)

Timing diagram for Figure 317 showing counter behavior with ARPE = 0.

This timing diagram illustrates the operation of a counter when ARPE = 0 and the TIMx_ARR register is not preloaded. The signals shown are:

MS31082V2

Timing diagram for Figure 317 showing counter behavior with ARPE = 0.

Figure 318. Counter timing diagram, update event when ARPE=1 (TIMx_ARR preloaded)

Figure 318. Counter timing diagram, update event when ARPE=1 (TIMx_ARR preloaded). The diagram shows the relationship between the prescaler clock (CK_PSC), enable signal (CEN), timer clock (CK_CNT), counter register values, counter overflow, update event (UEV), update interrupt flag (UIF), and auto-reload registers (ARR and shadow register).

The timing diagram illustrates the operation of a basic timer when ARPE=1. The signals shown are:

MS31083V2

Figure 318. Counter timing diagram, update event when ARPE=1 (TIMx_ARR preloaded). The diagram shows the relationship between the prescaler clock (CK_PSC), enable signal (CEN), timer clock (CK_CNT), counter register values, counter overflow, update event (UEV), update interrupt flag (UIF), and auto-reload registers (ARR and shadow register).

23.3.3 UIF bit remapping

The IUFREMAP bit in the TIMx_CR1 register forces a continuous copy of the Update Interrupt Flag UIF into the timer counter register's bit 31 (TIMxCNT[31]). This allows to atomically read both the counter value and a potential roll-over condition signaled by the UIFCPY flag. In particular cases, it can ease the calculations by avoiding race conditions caused for instance by a processing shared between a background task (counter reading) and an interrupt (Update Interrupt).

There is no latency between the assertions of the UIF and UIFCPY flags.

23.3.4 Clock source

The counter clock is provided by the Internal clock (CK_INT) source.

The CEN (in the TIMx_CR1 register) and UG bits (in the TIMx_EGR register) are actual control bits and can be changed only by software (except for UG that remains cleared automatically). As soon as the CEN bit is written to 1, the prescaler is clocked by the internal clock CK_INT.

Figure 319 shows the behavior of the control circuit and the upcounter in normal mode, without prescaler.

Figure 319. Control circuit in normal mode, internal clock divided by 1

Timing diagram showing the control circuit in normal mode. It displays five signals over time: Internal clock (a high-frequency square wave), CEN=CNT_EN (a signal that goes high to enable the counter), UG (a pulse that triggers an update), CNT_INIT (a pulse that initializes the counter), and Counter register (a sequence of values: 31, 32, 33, 34, 35, 36, 00, 01, 02, 03, 04, 05, 06, 07). Vertical dashed lines indicate the relationship between these signals. The counter register values are shown in a sequence of boxes, with the first box containing '31' and the last box containing '07'. The counter clock is labeled as CK_CNT = CK_PSC.

MS31085V2

Timing diagram showing the control circuit in normal mode. It displays five signals over time: Internal clock (a high-frequency square wave), CEN=CNT_EN (a signal that goes high to enable the counter), UG (a pulse that triggers an update), CNT_INIT (a pulse that initializes the counter), and Counter register (a sequence of values: 31, 32, 33, 34, 35, 36, 00, 01, 02, 03, 04, 05, 06, 07). Vertical dashed lines indicate the relationship between these signals. The counter register values are shown in a sequence of boxes, with the first box containing '31' and the last box containing '07'. The counter clock is labeled as CK_CNT = CK_PSC.

23.3.5 Debug mode

When the microcontroller enters the debug mode (Cortex®-M4 core - halted), the TIMx counter either continues to work normally or stops, depending on the DBG_TIMx_STOP configuration bit in the DBG module. For more details, refer to Section 31.15.2: Debug support for timers, watchdog, bxCAN and I 2 C .

23.4 TIM6/TIM7 registers

Refer to Section 1.2 on page 43 for a list of abbreviations used in register descriptions.

The peripheral registers can be accessed by half-words (16-bit) or words (32-bit).

23.4.1 TIMx control register 1 (TIMx_CR1)(x = 6 to 7)

Address offset: 0x00

Reset value: 0x0000

1514131211109876543210
Res.Res.Res.Res.UIFREMAPRes.Res.Res.ARPERes.Res.Res.OPMURSUDISCEN
rwrwrwrwrwrw

Bits 15:12 Reserved, must be kept at reset value.

Bit 11 UIFREMAP : UIF status bit remapping

0: No remapping. UIF status bit is not copied to TIMx_CNT register bit 31.

1: Remapping enabled. UIF status bit is copied to TIMx_CNT register bit 31.

Bits 10:8 Reserved, must be kept at reset value.

Bit 7 ARPE : Auto-reload preload enable

0: TIMx_ARR register is not buffered.

1: TIMx_ARR register is buffered.

Bits 6:4 Reserved, must be kept at reset value.

Bit 3 OPM : One-pulse mode

0: Counter is not stopped at update event

1: Counter stops counting at the next update event (clearing the CEN bit).

Bit 2 URS : Update request source

This bit is set and cleared by software to select the UEV event sources.

0: Any of the following events generates an update interrupt or DMA request if enabled.

These events can be:

1: Only counter overflow/underflow generates an update interrupt or DMA request if enabled.

Bit 1 UDIS : Update disable

This bit is set and cleared by software to enable/disable UEV event generation.

0: UEV enabled. The Update (UEV) event is generated by one of the following events:

Buffered registers are then loaded with their preload values.

1: UEV disabled. The Update event is not generated, shadow registers keep their value (ARR, PSC). However the counter and the prescaler are reinitialized if the UG bit is set or if a hardware reset is received from the slave mode controller.

Bit 0 CEN : Counter enable

0: Counter disabled

1: Counter enabled

Note: Gated mode can work only if the CEN bit has been previously set by software.

However trigger mode can set the CEN bit automatically by hardware.

CEN is cleared automatically in one-pulse mode, when an update event occurs.

23.4.2 TIMx control register 2 (TIMx_CR2)(x = 6 to 7)

Address offset: 0x04

Reset value: 0x0000

1514131211109876543210
Res.Res.Res.Res.Res.Res.Res.Res.Res.MMS[2:0]Res.Res.Res.Res.
rwrwrw

Bits 15:7 Reserved, must be kept at reset value.

Bits 6:4 MMS[2:0] : Master mode selection

These bits are used to select the information to be sent in master mode to slave timers for synchronization (TRGO). The combination is as follows:

000: Reset - the UG bit from the TIMx_EGR register is used as a trigger output (TRGO). If reset is generated by the trigger input (slave mode controller configured in reset mode) then the signal on TRGO is delayed compared to the actual reset.

001: Enable - the Counter enable signal, CNT_EN, is used as a trigger output (TRGO). It is useful to start several timers at the same time or to control a window in which a slave timer is enabled. The Counter Enable signal is generated by a logic OR between CEN control bit and the trigger input when configured in gated mode.

When the Counter Enable signal is controlled by the trigger input, there is a delay on TRGO, except if the master/slave mode is selected (see the MSM bit description in the TIMx_SMCR register).

010: Update - The update event is selected as a trigger output (TRGO). For instance a master timer can then be used as a prescaler for a slave timer.

Note: The clock of the slave timer or ADC must be enabled prior to receive events from the master timer, and must not be changed on-the-fly while triggers are received from the master timer.

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

23.4.3 TIMx DMA/Interrupt enable register (TIMx_DIER)(x = 6 to 7)

Address offset: 0x0C

Reset value: 0x0000

1514131211109876543210
Res.Res.Res.Res.Res.Res.Res.UDERes.Res.Res.Res.Res.Res.Res.UIE
rwrw

Bits 15:9 Reserved, must be kept at reset value.

Bit 8 UDE : Update DMA request enable

0: Update DMA request disabled.

1: Update DMA request enabled.

Bits 7:1 Reserved, must be kept at reset value.

Bit 0 UIE : Update interrupt enable

0: Update interrupt disabled.

1: Update interrupt enabled.

23.4.4 TIMx status register (TIMx_SR)(x = 6 to 7)

Address offset: 0x10

Reset value: 0x0000

1514131211109876543210
Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.UIF
rc_w0

Bits 15:1 Reserved, must be kept at reset value.

Bit 0 UIF : Update interrupt flag

This bit is set by hardware on an update event. It is cleared by software.

0: No update occurred.

1: Update interrupt pending. This bit is set by hardware when the registers are updated:

23.4.5 TIMx event generation register (TIMx_EGR)(x = 6 to 7)

Address offset: 0x14

Reset value: 0x0000

1514131211109876543210
Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.UG
w

Bits 15:1 Reserved, must be kept at reset value.

Bit 0 UG : Update generation

This bit can be set by software, it is automatically cleared by hardware.

0: No action.

1: Re-initializes the timer counter and generates an update of the registers. Note that the prescaler counter is cleared too (but the prescaler ratio is not affected).

23.4.6 TIMx counter (TIMx_CNT)(x = 6 to 7)

Address offset: 0x24

Reset value: 0x0000 0000

31302928272625242322212019181716
UIF
CPY
Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.
r

1514131211109876543210
CNT[15:0]
rwrwrwrwrwrwrwrwrwrwrwrwrwrwrwrw

Bit 31 UIFCPY : UIF Copy

This bit is a read-only copy of the UIF bit of the TIMx_ISR register. If the UIFREMAP bit in TIMx_CR1 is reset, bit 31 is reserved and read as 0.

Bits 30:16 Reserved, must be kept at reset value.

Bits 15:0 CNT[15:0] : Counter value

23.4.7 TIMx prescaler (TIMx_PSC)(x = 6 to 7)

Address offset: 0x28

Reset value: 0x0000

1514131211109876543210
PSC[15:0]
rwrwrwrwrwrwrwrwrwrwrwrwrwrwrwrw

Bits 15:0 PSC[15:0] : Prescaler value

The counter clock frequency \( CK\_CNT \) is equal to \( f_{CK\_PSC} / (PSC[15:0] + 1) \) .

PSC contains the value to be loaded into the active prescaler register at each update event. (including when the counter is cleared through UG bit of TIMx_EGR register or through trigger controller when configured in “reset mode”).

23.4.8 TIMx auto-reload register (TIMx_ARR)(x = 6 to 7)

Address offset: 0x2C

Reset value: 0xFFFF

1514131211109876543210
ARR[15:0]
rwrwrwrwrwrwrwrwrwrwrwrwrwrwrwrw

Bits 15:0 ARR[15:0] : Auto-reload value

ARR is the value to be loaded into the actual auto-reload register.

Refer to Section 23.3.1: Time-base unit on page 807 for more details about ARR update and behavior.

The counter is blocked while the auto-reload value is null.

23.4.9 TIMx register map

TIMx registers are mapped as 16-bit addressable registers as described in the table below:

Table 108. TIMx register map and reset values

OffsetRegister name313029282726252423222120191817161514131211109876543210
0x00TIMx_CR1Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.UIFREMARes.Res.Res.ARPERes.Res.Res.OPMURSUDISCEN
Reset value000000
0x04TIMx_CR2Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.MMS [2:0]Res.Res.Res.Res.
Reset value000
0x08Reserved
0x0CTIMx_DIERRes.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.UDERes.Res.Res.Res.Res.Res.Res.UIE
Reset value00
0x10TIMx_SRRes.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.UIF
Reset value0
0x14TIMx_EGRRes.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.UG
Reset value0
0x18-0x20Reserved
0x24TIMx_CNTUIFCOPY or Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.CNT[15:0]
Reset value00
0x28TIMx_PSCRes.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.PSC[15:0]
Reset value0
0x2CTIMx_ARRRes.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.Res.ARR[15:0]
Reset value1

Refer to Section 2.2 on page 47 for the register boundary addresses.