Z89175 Zilog., Z89175 Datasheet - Page 37

• Manufacturer Part Number: Z89175
• Description: Voice Processing Controllers
• Manufacturer: Zilog.

Zilog
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.
DS97TAD0100
C1
C2
Ceramic Resonator or
Crystal
XTAL1
XTAL2
Figure 23. Oscillator Configuration
P R E L I M I N A R Y
C1
C2
LC
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.
L
XTAL1
XTAL2
Voice Processing Controllers
External Clock
XTAL1
XTAL2
Z89175/Z89176
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