Z89175 Datasheet, PDF (37/68 Pages) Zilog, Inc. – Voice Processing Controllers

Zilog
Z89175/Z89176
Voice Processing Controllers
XTAL1
XTAL1
C1
C1
L
XTAL2
XTAL2
C2
C2
XTAL1
2
XTAL2
Ceramic Resonator or
LC
Crystal
Figure 23. Oscillator Configuration
External Clock
Counter/Timers. There are two 8-bit programmable
counter/timers (T1,T0), each driven by its own 6-bit pro-
grammable prescaler. The T1 prescaler is driven by inter-
nal or external clock sources. However, the T0 prescaler is
driven by the internal clock only (Figure 24).
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
(0 to 256) that has been loaded into the counter. When the
counter reaches the end of the count, a timer interrupt re-
quest, IRQ4 (T0) or IRQ5 (T1), is generated.
The counters can be programmed to start, stop, restart to
continue, or restart from the initial value. The counters can
also be programmed to stop upon reaching zero (single
pass mode) or to automatically reload the initial value and
continue counting (modulo-n continuous mode).
The counters, but not the prescalers, are read at any time
without disturbing their value or count mode. The clock
source for T1 is user-definable and is either the internal mi-
croprocessor clock divided by four, or an external signal in-
put via Port 31. The Timer Mode register configures the ex-
ternal timer input (P31) as an external clock, a trigger input
that can be retriggerable or non-retriggerable, or
as a gate input for the internal clock. The counter/timers
can be cascaded by connecting the T0 output to the input
of T1.
DS97TAD0100
PRELIMINARY
37