Texas Instruments MSP430x1xx manual Use of the Up/Down Mode, 9. Output Unit in Up/Down Mode

Timer_A Operation

Changing the Period Register TACCR0

When changing TACCR0 while the timer is running, and counting in the down direction, the timer continues its descent until it reaches zero. The new period takes affect after the counter counts down to zero.

When the timer is counting in the up direction, and the new period is greater than or equal to the old period, or greater than the current count value, the timer counts up to the new period before counting down. When the timer is counting in the up direction, and the new period is less than the current count value, the timer begins counting down. However, one additional count may occur before the counter begins counting down.

Use of the Up/Down Mode

The up/down mode supports applications that require dead times between output signals (See section Timer_A Output Unit). For example, to avoid overload conditions, two outputs driving an H-bridge must never be in a high state simultaneously. In the example shown in Figure 11−9 the t dead is:

tdead = ttimer ⋅ (TACCR1 − TACCR2)

With: tdead	Time during which both outputs need to be inactive
ttimer	Cycle time of the timer clock
TACCRx	Content of capture/compare register x

The TACCRx registers are not buffered. They update immediately when written to. Therefore, any required dead time will not be maintained automatically.

Figure 11−9. Output Unit in Up/Down Mode

0FFFFh
TACCR0
TACCR1
TACCR2
0h							Dead Time
							Output Mode 6: Toggle/Set
							Output Mode 2: Toggle/Reset
TAIFG	EQU1	EQU1	TAIFG		EQU1	EQU1	Interrupt Events
	EQU0				EQU0
EQU2		EQU2		EQU2		EQU2

11-10Timer_A