CP3BT26

26.2.3Mode 3: Dual Independent Timer/Counter

Mode 3 is the Dual Independent Timer mode, which gener- ates system timing signals or counts occurrences of exter- nal events.

Figure 102 is a block diagram of the Multi-Function Timer configured to operate in Mode 3. The timer is configured to operate as a dual independent system timer or dual external event counter. In addition, Timer/Counter 1 can generate a 50% duty cycle PWM signal on the TA pin. The TB pin can be used as an external event input or pulse-accumulate in- put and can be used as the clock source for either Timer/ Counter 1 or Timer/Counter 2. Both counters can also be clocked by the prescaled System Clock.

Timer/Counter 1 (TCNT1) counts down at the rate of the se- lected clock. On underflow, it is reloaded from the TCRA register and counting proceeds down from the reloaded val-

ue. In addition, the TA pin is toggled on each underflow if this function is enabled by the TAEN bit. The initial state of the TA pin is software-programmable. When the TA pin is tog- gled from low to high, it sets the TCPND interrupt pending bit and also generates an interrupt if enabled by the TAIEN bit.

Because the TA pin toggles on every underflow, a 50% duty cycle PWM signal can be generated on the TA pin without any further action from the CPU.

Timer/Counter 2 (TCNT2) counts down at the rate of the se- lected clock. On underflow, it is reloaded from the TCRB register and counting proceeds down from the reloaded val- ue. In addition, each underflow sets the TDPND interrupt pending bit and generates an interrupt if the interrupt is en- abled by the TDIEN bit.

Timer 1

Clock

Timer 2

Clock

Clock Selector

Reload A

TCRA

Underflow

Timer/Counter 1

TCNT1

Reload B

TCRB

Underflow

Timer/Counter 2

TCNT2

TAPND

Timer

Interrupt 1

TAIEN

TA

TAEN

Timer

Interrupt 2

TDIEN

TDPND

TB

DS086

Figure 102. Dual-Independent Timer/Counter Mode

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National CP3BT26 manual Mode 3 Dual Independent Timer/Counter, 200