IBM EM78P809N manual Timer Mode, Counter Mode, Window Mode

EM78P809N

8-Bit Microcontroller

4.9.1 Timer Mode:

In Timer mode, counting up is performed using the internal clock. When the contents of the up-counter matched with the TCR2 (TCR2H+TCR2L), then interrupt is generated and the counter is cleared. Counting up resumes after the counter is cleared.

Internal clock

Up-counter	0 1	2	3	4	5	n-3 n-2 n-1	n 0 1 2	3
TCR2	n					match	counter
							clear

TC2 interrupt

Fig. 20. Timer Mode Timing Chart

4.9.2 Counter Mode:

In Counter mode, counting up is performed using the external clock input pin (TC2 pin) and either rising or falling can be selected by setting TC2ES. When the contents of the up-counter matched with the TCR2 (TCR2H+TCR2L), then interrupt is generated and the counter is cleared. Counting up resumes after the counter is cleared.

TC2 Pin

Up-counter	0 1	2	3	4	n-2	n-1 n 0	1 2	3
TCR2	n					match	counter
							clear

TC2 interrupt

Fig. 21. Counter Mode Timing Chart (TC2ES = 1)

4.9.3 Window Mode

In Window mode, counting up is performed on the rising or falling edge of the pulse that is logical AND of an internal clock and the TC2 pin (window pulse). When the contents of the up-counter matched with the TCR2 (TCR2H+TCR2L), then interrupt is generated and the counter is cleared. The frequency (window pulse) must be slower than the selected internal clock.

Writing to the TCR2L, the comparison is inhibited until TCR2H is written.

Product Specification (V1.0) 07.26.2005 • 41

(This specification is subject to change without further notice)