Specifications

Counter/Timers
Mode 4 - Software Triggered Strobe
Mode 4 operation provides a means of generating a hardware delay
triggered by software. Counter/timer 2 fully supports Mode 4
operation with the TCTL input available through connector J3 of the
ZT 8832. Counter/timers 0 and 1 support Mode 4 with the exception
of the TCTL input signal.
Examples of Mode 4 operation are included in Figure 7-11. Counting
begins automatically one clock pulse after the count is programmed.
TOUT remains high until the count reaches zero. At a count of zero,
TOUT goes low for one clock pulse and returns high. The count is not
decremented until after it is transferred to the Down Counter by the
first clock pulse. This means TOUT does not go low until N + 1 clock
pulses later, for an initial count of N.
The TCTL signal can be used to stop the Down Counter for
counter/timer 2. A high TCTL signal enables counting and a low on
TCTL stops it. TOUT is not affected by TCTL.
A new count can be written to the counter/timer while it is counting.
The new count will be transferred to the Down Counter on the next
clock pulse and counting will continue from the new value. A two-
byte count will not be transferred to the Down Counter until the
second byte is written.
7-24