TIMER - Timer/Counter#

Timer/Counter (TIMER) Peripheral API.

The timer module consists of three main parts:

General timer configuration and enable control.
Compare/capture control.
Dead time insertion control (may not be available for all timers).

Modules#

TIMER_Init_TypeDef

TIMER_InitCC_TypeDef

TIMER_InitDTI_TypeDef

Enumerations#

enum

TIMER_CCMode_TypeDef {

timerCCModeOff = _TIMER_CC_CFG_MODE_OFF

timerCCModeCapture = _TIMER_CC_CFG_MODE_INPUTCAPTURE

timerCCModeCompare = _TIMER_CC_CFG_MODE_OUTPUTCOMPARE

timerCCModePWM = _TIMER_CC_CFG_MODE_PWM

}

Timer compare/capture mode.

enum

TIMER_ClkSel_TypeDef {

timerClkSelHFPerClk = _TIMER_CFG_CLKSEL_PRESCEM01GRPACLK

timerClkSelCC1 = _TIMER_CFG_CLKSEL_CC1

timerClkSelCascade = _TIMER_CFG_CLKSEL_TIMEROUF

}

Clock select.

enum

TIMER_Edge_TypeDef {

timerEdgeRising = _TIMER_CC_CTRL_ICEDGE_RISING

timerEdgeFalling = _TIMER_CC_CTRL_ICEDGE_FALLING

timerEdgeBoth = _TIMER_CC_CTRL_ICEDGE_BOTH

timerEdgeNone = _TIMER_CC_CTRL_ICEDGE_NONE

}

Input capture edge select.

enum

TIMER_Event_TypeDef {

timerEventEveryEdge = _TIMER_CC_CTRL_ICEVCTRL_EVERYEDGE

timerEventEvery2ndEdge = _TIMER_CC_CTRL_ICEVCTRL_EVERYSECONDEDGE

timerEventRising = _TIMER_CC_CTRL_ICEVCTRL_RISING

timerEventFalling = _TIMER_CC_CTRL_ICEVCTRL_FALLING

}

Input capture event control.

enum

TIMER_InputAction_TypeDef {

timerInputActionNone = _TIMER_CTRL_FALLA_NONE

timerInputActionStart = _TIMER_CTRL_FALLA_START

timerInputActionStop = _TIMER_CTRL_FALLA_STOP

timerInputActionReloadStart = _TIMER_CTRL_FALLA_RELOADSTART

}

Input edge action.

enum

TIMER_Mode_TypeDef {

timerModeUp = _TIMER_CFG_MODE_UP

timerModeDown = _TIMER_CFG_MODE_DOWN

timerModeUpDown = _TIMER_CFG_MODE_UPDOWN

timerModeQDec = _TIMER_CFG_MODE_QDEC

}

Timer mode.

enum

TIMER_OutputAction_TypeDef {

timerOutputActionNone = _TIMER_CC_CTRL_CUFOA_NONE

timerOutputActionToggle = _TIMER_CC_CTRL_CUFOA_TOGGLE

timerOutputActionClear = _TIMER_CC_CTRL_CUFOA_CLEAR

timerOutputActionSet = _TIMER_CC_CTRL_CUFOA_SET

}

Compare/capture output action.

enum

TIMER_Prescale_TypeDef {

timerPrescale1 = _TIMER_CFG_PRESC_DIV1

timerPrescale2 = _TIMER_CFG_PRESC_DIV2

timerPrescale4 = _TIMER_CFG_PRESC_DIV4

timerPrescale8 = _TIMER_CFG_PRESC_DIV8

timerPrescale16 = _TIMER_CFG_PRESC_DIV16

timerPrescale32 = _TIMER_CFG_PRESC_DIV32

timerPrescale64 = _TIMER_CFG_PRESC_DIV64

timerPrescale128 = _TIMER_CFG_PRESC_DIV128

timerPrescale256 = _TIMER_CFG_PRESC_DIV256

timerPrescale512 = _TIMER_CFG_PRESC_DIV512

timerPrescale1024 = _TIMER_CFG_PRESC_DIV1024

}

Prescaler.

enum

TIMER_PrsInput_TypeDef {

timerPrsInputNone = 0x0

timerPrsInputSync = _TIMER_CC_CFG_INSEL_PRSSYNC

timerPrsInputAsyncLevel = _TIMER_CC_CFG_INSEL_PRSASYNCLEVEL

timerPrsInputAsyncPulse = _TIMER_CC_CFG_INSEL_PRSASYNCPULSE

}

PRS input type.

enum

TIMER_DtiFaultAction_TypeDef {

timerDtiFaultActionNone = _TIMER_DTFCFG_DTFA_NONE

timerDtiFaultActionInactive = _TIMER_DTFCFG_DTFA_INACTIVE

timerDtiFaultActionClear = _TIMER_DTFCFG_DTFA_CLEAR

timerDtiFaultActionTristate = _TIMER_DTFCFG_DTFA_TRISTATE

}

DT (Dead Time) Fault Actions.

enum

TIMER_PrsOutput_t {

timerPrsOutputPulse = 0

timerPrsOutputLevel = 1

timerPrsOutputDefault = timerPrsOutputPulse

}

PRS Output configuration.

Typedefs#

typedef uint8_t

TIMER_PRSSEL_TypeDef

Peripheral Reflex System signal.

Functions#

void

TIMER_Init(TIMER_TypeDef *timer, const TIMER_Init_TypeDef *init)

Initialize TIMER.

void

TIMER_InitCC(TIMER_TypeDef *timer, unsigned int ch, const TIMER_InitCC_TypeDef *init)

Initialize the TIMER compare/capture channel.

void

TIMER_InitDTI(TIMER_TypeDef *timer, const TIMER_InitDTI_TypeDef *init)

Initialize the TIMER DTI unit.

void

TIMER_Reset(TIMER_TypeDef *timer)

Reset the TIMER to the same state that it was in after a hardware reset.

void

TIMER_SyncWait(TIMER_TypeDef *timer)

Wait for pending synchronization to finish.

bool

TIMER_Valid(const TIMER_TypeDef *ref)

Validate the TIMER register block pointer.

bool

TIMER_SupportsDTI(const TIMER_TypeDef *ref)

Check whether the TIMER is valid and supports Dead Timer Insertion (DTI).

uint32_t

TIMER_MaxCount(const TIMER_TypeDef *ref)

Get the Max count of the timer.

uint32_t

TIMER_CaptureGet(TIMER_TypeDef *timer, unsigned int ch)

Get compare/capture value for the compare/capture channel.

uint32_t

TIMER_CaptureBufGet(TIMER_TypeDef *timer, unsigned int ch)

Get the buffered compare/capture value for compare/capture channel.

void

TIMER_CompareBufSet(TIMER_TypeDef *timer, unsigned int ch, uint32_t val)

Set the compare value buffer for the compare/capture channel when operating in compare or PWM mode.

void

TIMER_CompareSet(TIMER_TypeDef *timer, unsigned int ch, uint32_t val)

Set the compare value for compare/capture channel when operating in compare or PWM mode.

uint32_t

TIMER_CounterGet(TIMER_TypeDef *timer)

Get the TIMER counter value.

void

TIMER_CounterSet(TIMER_TypeDef *timer, uint32_t val)

Set the TIMER counter value.

void

TIMER_Enable(TIMER_TypeDef *timer, bool enable)

Start/stop TIMER.

void

TIMER_EnableDTI(TIMER_TypeDef *timer, bool enable)

Enable or disable DTI unit.

uint32_t

TIMER_GetDTIFault(TIMER_TypeDef *timer)

Get DTI fault source flags status.

void

TIMER_ClearDTIFault(TIMER_TypeDef *timer, uint32_t flags)

Clear DTI fault source flags.

void

TIMER_IntClear(TIMER_TypeDef *timer, uint32_t flags)

Clear one or more pending TIMER interrupts.

void

TIMER_IntDisable(TIMER_TypeDef *timer, uint32_t flags)

Disable one or more TIMER interrupts.

void

TIMER_IntEnable(TIMER_TypeDef *timer, uint32_t flags)

Enable one or more TIMER interrupts.

uint32_t

TIMER_IntGet(TIMER_TypeDef *timer)

Get pending TIMER interrupt flags.

uint32_t

TIMER_IntGetEnabled(TIMER_TypeDef *timer)

Get enabled and pending TIMER interrupt flags.

void

TIMER_IntSet(TIMER_TypeDef *timer, uint32_t flags)

Set one or more pending TIMER interrupts from SW.

void

TIMER_TopBufSet(TIMER_TypeDef *timer, uint32_t val)

Set the top value buffer for the timer.

uint32_t

TIMER_TopGet(TIMER_TypeDef *timer)

Get the top value setting for the timer.

void

TIMER_TopSet(TIMER_TypeDef *timer, uint32_t val)

Set the top value for timer.

Macros#

#define

TIMER_INIT_DEFAULT undefined

Default configuration for TIMER initialization structure.

#define

TIMER_INITCC_DEFAULT undefined

Default configuration for TIMER compare/capture initialization structure.

#define

TIMER_INITDTI_DEFAULT undefined

Default configuration for TIMER DTI initialization structure.

Enumeration Documentation#

TIMER_CCMode_TypeDef#

TIMER_CCMode_TypeDef

Timer compare/capture mode.

Enumerator
timerCCModeOff	Channel turned off.
timerCCModeCapture	Input capture.
timerCCModeCompare	Output compare.
timerCCModePWM	Pulse-Width modulation.

TIMER_ClkSel_TypeDef#

TIMER_ClkSel_TypeDef

Clock select.

Enumerator
timerClkSelHFPerClk	Prescaled EM01GRPA clock.
timerClkSelCC1	Compare/Capture Channel 1 Input.
timerClkSelCascade	Cascaded clocked by underflow or overflow by lower numbered timer.

TIMER_Edge_TypeDef#

TIMER_Edge_TypeDef

Input capture edge select.

Enumerator
timerEdgeRising	Rising edges detected.
timerEdgeFalling	Falling edges detected.
timerEdgeBoth	Both edges detected.
timerEdgeNone	No edge detection, leave signal as is.

TIMER_Event_TypeDef#

TIMER_Event_TypeDef

Input capture event control.

Enumerator
timerEventEveryEdge	PRS output pulse, interrupt flag, and DMA request set on every capture.
timerEventEvery2ndEdge	PRS output pulse, interrupt flag, and DMA request set on every second capture.
timerEventRising	PRS output pulse, interrupt flag, and DMA request set on rising edge (if input capture edge = BOTH).
timerEventFalling	PRS output pulse, interrupt flag, and DMA request set on falling edge (if input capture edge = BOTH).

TIMER_InputAction_TypeDef#

TIMER_InputAction_TypeDef

Input edge action.

Enumerator
timerInputActionNone	No action taken.
timerInputActionStart	Start counter without reload.
timerInputActionStop	Stop counter without reload.
timerInputActionReloadStart	Reload and start counter.

TIMER_Mode_TypeDef#

TIMER_Mode_TypeDef

Timer mode.

Enumerator
timerModeUp	Up-counting.
timerModeDown	Down-counting.
timerModeUpDown	Up/down-counting.
timerModeQDec	Quadrature decoder.

TIMER_OutputAction_TypeDef#

TIMER_OutputAction_TypeDef

Compare/capture output action.

Enumerator
timerOutputActionNone	No action.
timerOutputActionToggle	Toggle on event.
timerOutputActionClear	Clear on event.
timerOutputActionSet	Set on event.

TIMER_Prescale_TypeDef#

TIMER_Prescale_TypeDef

Prescaler.

Enumerator
timerPrescale1	Divide by 1.
timerPrescale2	Divide by 2.
timerPrescale4	Divide by 4.
timerPrescale8	Divide by 8.
timerPrescale16	Divide by 16.
timerPrescale32	Divide by 32.
timerPrescale64	Divide by 64.
timerPrescale128	Divide by 128.
timerPrescale256	Divide by 256.
timerPrescale512	Divide by 512.
timerPrescale1024	Divide by 1024.

TIMER_PrsInput_TypeDef#

TIMER_PrsInput_TypeDef

PRS input type.

Enumerator
timerPrsInputNone	No PRS input.
timerPrsInputSync	Synchronous PRS selected.
timerPrsInputAsyncLevel	Asynchronous level PRS selected.
timerPrsInputAsyncPulse	Asynchronous pulse PRS selected.

TIMER_DtiFaultAction_TypeDef#

TIMER_DtiFaultAction_TypeDef

DT (Dead Time) Fault Actions.

Enumerator
timerDtiFaultActionNone	No action on fault.
timerDtiFaultActionInactive	Set outputs inactive.
timerDtiFaultActionClear	Clear outputs.
timerDtiFaultActionTristate	Tristate outputs.

TIMER_PrsOutput_t#

TIMER_PrsOutput_t

PRS Output configuration.

Enumerator
timerPrsOutputPulse	Pulse PRS output from a channel.
timerPrsOutputLevel	PRS output follows CC out level.
timerPrsOutputDefault	Default PRS output behavior.

Typedef Documentation#

TIMER_PRSSEL_TypeDef#

typedef uint8_t TIMER_PRSSEL_TypeDef

Peripheral Reflex System signal.

Function Documentation#

TIMER_Init#

void TIMER_Init (TIMER_TypeDef * timer, const TIMER_Init_TypeDef * init)

Initialize TIMER.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	A pointer to the TIMER peripheral register block.
const TIMER_Init_TypeDef *	[in]	init	A pointer to the TIMER initialization structure.

Notice that the counter top must be configured separately with, for instance TIMER_TopSet(). In addition, compare/capture and dead-time insertion initialization must be initialized separately if used, which should probably be done prior to using this function if configuring the TIMER to start when initialization is completed.

TIMER_InitCC#

void TIMER_InitCC (TIMER_TypeDef * timer, unsigned int ch, const TIMER_InitCC_TypeDef * init)

Initialize the TIMER compare/capture channel.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	A pointer to the TIMER peripheral register block.
unsigned int	[in]	ch	A compare/capture channel to initialize for.
const TIMER_InitCC_TypeDef *	[in]	init	A pointer to the TIMER initialization structure.

Notice that if operating the channel in compare mode, the CCV and CCVB register must be set separately, as required.

TIMER_InitDTI#

void TIMER_InitDTI (TIMER_TypeDef * timer, const TIMER_InitDTI_TypeDef * init)

Initialize the TIMER DTI unit.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	A pointer to the TIMER peripheral register block.
const TIMER_InitDTI_TypeDef *	[in]	init	A pointer to the TIMER DTI initialization structure.

TIMER_Reset#

void TIMER_Reset (TIMER_TypeDef * timer)

Reset the TIMER to the same state that it was in after a hardware reset.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	A pointer to the TIMER peripheral register block.

Note

The ROUTE register is NOT reset by this function to allow for a centralized setup of this feature.

TIMER_SyncWait#

void TIMER_SyncWait (TIMER_TypeDef * timer)

Wait for pending synchronization to finish.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer

TIMER_Valid#

bool TIMER_Valid (const TIMER_TypeDef * ref)

Validate the TIMER register block pointer.

Parameters

Type	Direction	Argument Name	Description
const TIMER_TypeDef *	[in]	ref	Pointer to the TIMER peripheral register block.

Returns

True if ref points to a valid timer, false otherwise.

TIMER_SupportsDTI#

bool TIMER_SupportsDTI (const TIMER_TypeDef * ref)

Check whether the TIMER is valid and supports Dead Timer Insertion (DTI).

Parameters

Type	Direction	Argument Name	Description
const TIMER_TypeDef *	[in]	ref	Pointer to the TIMER peripheral register block.

Returns

True if ref points to a valid timer that supports DTI, false otherwise.

TIMER_MaxCount#

uint32_t TIMER_MaxCount (const TIMER_TypeDef * ref)

Get the Max count of the timer.

Parameters

Type	Direction	Argument Name	Description
const TIMER_TypeDef *	[in]	ref	Pointer to the TIMER peripheral register block.

Returns

The max count value of the timer. This is 0xFFFF for 16 bit timers and 0xFFFFFFFF for 32 bit timers.

TIMER_CaptureGet#

uint32_t TIMER_CaptureGet (TIMER_TypeDef * timer, unsigned int ch)

Get compare/capture value for the compare/capture channel.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
unsigned int	[in]	ch	Compare/capture channel to access.

Returns

Current capture value.

TIMER_CaptureBufGet#

uint32_t TIMER_CaptureBufGet (TIMER_TypeDef * timer, unsigned int ch)

Get the buffered compare/capture value for compare/capture channel.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
unsigned int	[in]	ch	Compare/capture channel to access.

Returns

Current buffered capture value.

TIMER_CompareBufSet#

void TIMER_CompareBufSet (TIMER_TypeDef * timer, unsigned int ch, uint32_t val)

Set the compare value buffer for the compare/capture channel when operating in compare or PWM mode.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
unsigned int	[in]	ch	Compare/capture channel to access.
uint32_t	[in]	val	Value to set in compare value buffer register.

The compare value buffer holds the value which will be written to TIMERn_CCx_CCV on an update event if the buffer has been updated since the last event.

TIMER_CompareSet#

void TIMER_CompareSet (TIMER_TypeDef * timer, unsigned int ch, uint32_t val)

Set the compare value for compare/capture channel when operating in compare or PWM mode.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
unsigned int	[in]	ch	Compare/capture channel to access.
uint32_t	[in]	val	Value to set in compare value register.

TIMER_CounterGet#

uint32_t TIMER_CounterGet (TIMER_TypeDef * timer)

Get the TIMER counter value.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to TIMER peripheral register block.

Returns

Current TIMER counter value.

TIMER_CounterSet#

void TIMER_CounterSet (TIMER_TypeDef * timer, uint32_t val)

Set the TIMER counter value.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	val	Value to set counter to.

TIMER_Enable#

void TIMER_Enable (TIMER_TypeDef * timer, bool enable)

Start/stop TIMER.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
bool	[in]	enable	Set to true to enable counting; set to false otherwise.

TIMER_EnableDTI#

void TIMER_EnableDTI (TIMER_TypeDef * timer, bool enable)

Enable or disable DTI unit.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
bool	[in]	enable	Set to true to enable DTI unit; set to false otherwise.

TIMER_GetDTIFault#

uint32_t TIMER_GetDTIFault (TIMER_TypeDef * timer)

Get DTI fault source flags status.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.

Note

Event bits are not cleared by this function.

Returns

Status of the DTI fault source flags. Returns one or more valid DTI fault source flags (TIMER_DTFAULT_nnn) OR'ed together.

TIMER_ClearDTIFault#

void TIMER_ClearDTIFault (TIMER_TypeDef * timer, uint32_t flags)

Clear DTI fault source flags.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	flags	DTI fault source(s) to clear. Use one or more valid DTI fault source flags (TIMER_DTFAULT_nnn) OR'ed together.

TIMER_IntClear#

void TIMER_IntClear (TIMER_TypeDef * timer, uint32_t flags)

Clear one or more pending TIMER interrupts.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	flags	Pending TIMER interrupt source(s) to clear. Use one or more valid interrupt flags for the TIMER module (TIMER_IF_nnn) OR'ed together.

TIMER_IntDisable#

void TIMER_IntDisable (TIMER_TypeDef * timer, uint32_t flags)

Disable one or more TIMER interrupts.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	flags	TIMER interrupt source(s) to disable. Use one or more valid interrupt flags for the TIMER module (TIMER_IF_nnn) OR'ed together.

TIMER_IntEnable#

void TIMER_IntEnable (TIMER_TypeDef * timer, uint32_t flags)

Enable one or more TIMER interrupts.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	flags	TIMER interrupt source(s) to enable. Use one or more valid interrupt flags for the TIMER module (TIMER_IF_nnn) OR'ed together.

Note

Depending on the use, a pending interrupt may already be set prior to enabling the interrupt. To ignore a pending interrupt, consider using TIMER_IntClear() prior to enabling the interrupt.

TIMER_IntGet#

uint32_t TIMER_IntGet (TIMER_TypeDef * timer)

Get pending TIMER interrupt flags.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.

Note

Event bits are not cleared by this function.

Returns

TIMER interrupt source(s) pending. Returns one or more valid interrupt flags for the TIMER module (TIMER_IF_nnn) OR'ed together.

TIMER_IntGetEnabled#

uint32_t TIMER_IntGetEnabled (TIMER_TypeDef * timer)

Get enabled and pending TIMER interrupt flags.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.

Useful for handling more interrupt sources in the same interrupt handler.

Note

Interrupt flags are not cleared by this function.

Returns

Pending and enabled TIMER interrupt sources. The return value is the bitwise AND combination of
- the OR combination of enabled interrupt sources in TIMERx_IEN_nnn register (TIMERx_IEN_nnn) and
- the OR combination of valid interrupt flags of the TIMER module (TIMERx_IF_nnn).

TIMER_IntSet#

void TIMER_IntSet (TIMER_TypeDef * timer, uint32_t flags)

Set one or more pending TIMER interrupts from SW.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	flags	TIMER interrupt source(s) to set to pending. Use one or more valid interrupt flags for the TIMER module (TIMER_IF_nnn) OR'ed together.

TIMER_TopBufSet#

void TIMER_TopBufSet (TIMER_TypeDef * timer, uint32_t val)

Set the top value buffer for the timer.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	val	Value to set in top value buffer register.

When top value buffer register is updated, value is loaded into top value register at the next wrap around. This feature is useful in order to update top value safely when timer is running.

TIMER_TopGet#

uint32_t TIMER_TopGet (TIMER_TypeDef * timer)

Get the top value setting for the timer.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.

Returns

Current top value.

TIMER_TopSet#

void TIMER_TopSet (TIMER_TypeDef * timer, uint32_t val)

Set the top value for timer.

Parameters

Type	Direction	Argument Name	Description
TIMER_TypeDef *	[in]	timer	Pointer to the TIMER peripheral register block.
uint32_t	[in]	val	Value to set in top value register.