Texas Instruments MSP430x1xx manual Changing the Period Register TBCL0

Timer_B Operation

Up Mode

The up mode is used if the timer period must be different from TBR(max) counts. The timer repeatedly counts up to the value of compare latch TBCL0, which

defines the period, as shown in Figure 12−2. The number of timer counts in the period is TBCL0+1. When the timer value equals TBCL0 the timer restarts counting from zero. If up mode is selected when the timer value is greater than TBCL0, the timer immediately restarts counting from zero.

Figure 12−2. Up Mode

TBR(max)

TBCL0

0h

The TBCCR0 CCIFG interrupt flag is set when the timer counts to the TBCL0 value. The TBIFG interrupt flag is set when the timer counts from TBCL0 to zero. Figure 11−3 shows the flag set cycle.

Figure 12−3. Up Mode Flag Setting

Timer Clock
Timer	TBCL0−1 TBCL0	0h	1h	TBCL0−1 TBCL0	0h
Set TBIFG

Set TBCCR0 CCIFG

Changing the Period Register TBCL0

When changing TBCL0 while the timer is running and when the TBCL0 load mode is immediate, if 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. If the new period is less than the current count value, the timer rolls to zero. However, one additional count may occur before the counter rolls to zero.

12-6Timer_B