Specifications

Counter/Timers
Mode 5 - Hardware Triggered Strobe
Mode 5 operation provides a means of generating a hardware delay
triggered by a hardware signal. This mode is similar to Mode 4 except
for the counting process, which is started by a signal external to the
ZT 8832. Counter/timer 2 is the only one that supports Mode 5.
Examples of Mode 5 operation are illustrated in Figure 7-12. A TCTL
trigger transfers the programmed count from the Count Latch to the
Down Counter and starts the counting process. The TOUT signal
remains until the count reaches zero. At a count of zero, TOUT goes
low for one clock pulse before returning high. It takes one clock pulse
to transfer the initial count from the Count Latch to the Down
Counter. This means for an initial count of N, TOUT will not go low
until N + 1 clock pulses after the TCTL trigger.
The counting sequence can be retriggered at any time with TCTL. If a
TCTL trigger occurs while the Down Counter is operating, the
programmed count is transferred to the Down Counter on the next
clock pulse and counting starts over. Writing a new count will not
affect counter/timer operation. If a TCTL trigger occurs after a new
count is programmed but before the current count expires, the new
count will be loaded and counting will begin at this new value.
7-26