Z86E61 Zilog., Z86E61 Datasheet - Page 15

• Manufacturer Part Number: Z86E61
• Description: CMOS Z8 16K/32K EPROM MICROCONTROLLER
• Manufacturer: Zilog.

FUNCTIONAL DESCRIPTION
Counter/Timers. There are two 8-bit programmable
counter/timers (T0-T1), 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 15).
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
the counters and prescalers reach the end of the count,
a timer interrupt request, IRQ4 (T0) or IRQ5 (T1), is
generated.
The counter is programmed to start, stop, restart to con-
tinue, or restart from the initial value. The counters can also
Tin P31
Clock
Logic
OSC
2
External Clock
Internal Clock
Gated Clock
Triggered Clock
Internal
Clock
4
Figure 15. Counter/Timers Block Diagram
4
Write
Write
P R E L I M I N A R Y
Initial Value
Initial Value
Register
Register
Counter
Counter
PRE0
Down
Down
PRE1
6-Bit
6-Bit
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 counter, 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
microprocessor clock divided-by-four, or an external sig-
nal input through Port 3. The Timer Mode register config-
ures the external 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. Port 3 line P36 also
serves as a timer output (T
internal clock can be output. The counter/timers are 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
Read
Read
2
OUT
Current Value
Current Value
Register
Register
) through which T0, T1, or the
T0
T1
IRQ4
Serial I/O
Clock
TOUT
P36
IRQ5
WITH
Z86E61/E63 Z8
16K/32K EPROM
®
MCU
15