Specifications

Introduction
Counter/Timers
The ZT 8809A has three independent 16-bit counter/timers, each of
which can be used as a timer or event counter. The clock frequency
driving each of these timers is a 1.19318 MHz oscillator. For timers 1
and 2, the clock input may be jumpered to receive the frontplane
connector J4 signal, which may be an external frequency or event
input.
The six programmable counter/timer modes are as follows:
1. Interrupt on end of count
2. Frequency divider
3. Square wave generator
4. Software triggered strobe
5. Retriggerable hardware triggered strobe
6. Retriggerable one-shot
Each timer output may be jumper-selected to drive one of the
interrupt controller inputs, and is also available at connector J4. The
"gate" or enable input to each timer is pulled up active by a 10 kΩ
resistor and may be controlled by a source on frontplane connector J4.
1-10