National CP3BT26 manual Timer Interrupts, Timer I/O Functions, Taen, Tben

CP3BT26

26.3TIMER INTERRUPTS

The Multi-Function Timer unit has four interrupt sources, designated A, B, C, and D. Interrupt sources A, B, and C are mapped into a single system interrupt called Timer Interrupt 1, while interrupt source D is mapped into a system interrupt called Timer Interrupt 2. Each of the four interrupt sources has its own enable bit and pending bit. The enable bits are named TAIEN, TBIEN, TCIEN, and TDIEN. The pending bits are named TAPND, TBPND, TCPND, and TDPND.

Timer Interrupts 1 and 2 are system interrupts TA and TB (IRQ14 and IRQ13), respectively.

Table 77 shows the events that trigger interrupts A, B, C, and D in each of the four operating modes. Note that some interrupt sources are not used in some operating modes.

26.4TIMER I/O FUNCTIONS

The Multi-Function Timer unit uses two I/O pins, called TA and TB. The function of each pin depends on the timer op- erating mode and the TAEN and TBEN enable bits. Table 78 shows the functions of the pins in each operating mode, and for each combination of enable bit settings.

When the TA pin is configured to operate as a PWM output (TAEN = 1), the state of the pin is toggled on each underflow of the TCNT1 counter. In this case, the initial value on the pin is determined by the TAOUT bit. For example, to start with TA high, software must set the TAOUT bit before en- abling the timer clock. This option is available only when the timer is configured to operate in Mode 1, 3, or 4 (in other words, when TCRA is not used in Capture mode).

Table 77 Timer Interrupts Overview

		Interrupt	Mode 1		Mode 2		Mode 3		Mode 4
Sys. Int.		Pending	PWM + Counter		Dual Input Capture +		Dual Counter		Single Capture +
		Bit
					Counter				Counter
Timer		TAPND	TCNT1 reload from		Input capture on TA		TCNT1 reload from		TCNT1 reload from
Int. 1			TCRA		transition		TCRA		TCRA
(TA Int.)
		TBPND	TCNT1 reload from		Input Capture on TB		N/A		Input Capture on TB
			TCRB		transition				transition
		TCPND	N/A		TCNT1 underflow		N/A		N/A
Timer		TDPND	TCNT2 underflow		TCNT2 underflow		TCNT2 reload from		TCNT2 underflow
Int. 2							TCRB
(TB Int.)
			Table 78 Timer I/O Functions
		TAEN	Mode 1		Mode 2		Mode 3		Mode 4
I/O
					Dual Input Capture +				Single Capture +
		TBEN	PWM + Counter				Dual Counter
					counter				counter
TA	TAEN = 0		No Output	Capture TCNT1 into		No Output Toggle		No Output Toggle
	TBEN = X			TCRA
	TAEN = 1		Toggle Output on	Capture TCNT1 into		Toggle Output on		Toggle Output on
	TBEN = X		Underflow of TCNT1	TCRA and Preset		Underflow of TCNT1		Underflow of TCNT1
				TCNT1
TB	TAEN = X		Ext. Event or Pulse	Capture TCNT1 into		Ext. Event or Pulse		Capture TCNT2 into
	TBEN = 0		Accumulate Input	TCRB		Accumulate Input		TCRB
	TAEN = X		Ext. Event or Pulse	Capture TCNT1 into		Ext. Event or Pulse		Capture TCNT2 into
	TBEN = 1		Accumulate Input	TCRB and Preset		Accumulate Input		TCRB and Preset
				TCNT1				TCNT2

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