Z86319 Datasheet, PDF (15/23 Pages) Zilog, Inc. – PS/2 MOUSE CONTROLLER

Zilog
Z86319
PS/2 Mouse Controller
Stack Pointer. The Z86319 features an 8-bit Stack The counter can be programmed to start, stop, continue,
Pointer (R255) used for the internal stack that resides with- or restart from the initial value. The counters can also be
in the general-purpose registers.
1 ^{programmed to stop upon reaching zero (single pass}
mode) or to automatically reload the initial value and contin-
Counter/Timer. There are two 8-bit programmable _{ue counting (modulo-n continuous mode).}
counter/timers (T0 and T1), each driven by its own 6-bit
programmable prescaler. The T1 prescaler can be driven The counters, but not the prescalers, are read at any time
by internal or external clock sources, however, the T0 can without disturbing their value or count mode. The clock
be driven by the internal clock source only (Figure 16).
source for T1 is user-definable and can be either the inter-
The 6-bit prescalers can divide the input frequency of the
clock source by any integer number from 1 to 64. Each
prescaler drives its counter, which decrements the value
(1 to 256) that has been loaded into the counter. When
both counter and prescaler reach the end of count, a timer
nal microprocessor clock divided by four, or an external
signal input via Port 3. The Timer Mode register configures
the external timer input (P31) as an external clock, a trigger
input that is retriggerable or not retriggerable, or as a gate
input for the internal clock.
interrupt request IRQ4 (T0) or IRQ5 (T1) is generated.
OSC
Internal
Clock
External Clock
Clock
Logic
÷4
Internal Data Bus
Write
Write
Read
PRE0
Initial Value
Register
T0
Initial Value
Register
T0
Current Value
Register
6-Bit
÷4
Down
Counter
8-Bit
Down
Counter
IRQ4
6-Bit
Down
Counter
8-Bit
Down
Counter
IRQ5
T_IN P31
Internal Clock
Gated Clock
Triggered Clock
PRE1
Initial Value
Register
T1
Initial Value
Register
T1
Current Value
Register
Write
Write
Read
Internal Data Bus
Figure 16. Counter/Timers Block Diagram
DS97KEY1605
PRELIMINARY
15