Z89139 Zilog., Z89139 Datasheet - Page 35

• Manufacturer Part Number: Z89139
• 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.
DS97TAD0201
(DSP CON)
D7, D6
(F) OC
DSP Clock
D0,D1
(SMR)
Clock
TIN P31
Logic
16
2
2
External Clock
Internal Clock
Gated Clock
Triggered Clock
Internal
Clock
4
2
Figure 24. Counter/Timer Block Diagram
T0, T2, T3
OSC
4
P R E L I M I N A R Y
Write
Write
Initial Value
Initial Value
Register
Register
Counter
Counter
PRE0
PRE1
Down
Down
6-Bit
6-Bit
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 cas-
caded by connecting the T0 output to the input of T1.
Write
Write
Internal Data Bus
Internal Data Bus
Initial Value
Initial Value
Register
Register
Counter
Counter
Down
Down
8-Bit
8-bit
T0
T1
Voice Processing Controllers
Read
Read
2
Current Value
Current Value
Register
Register
T0
T1
Z89138/Z89139
T
P36
IRQ5
IRQ4
OUT
35
1