Z86C83 Datasheet, PDF (25/46 Pages) Zilog, Inc. – Z8 MCU MICROCONTROLLERS

Z86C83/C84
Z8^® MCU Microcontrollers
FUNCTIONAL DESCRIPTION (Continued)
Counter/Timers. There are two 8-bit programmable
counter/timers (T0-T1), each driven by its own 6-bit
programmable prescaler. The T1 prescaler is driven by
internal or external clock sources; however, the T0
prescaler is driven by the internal clock only (Figure 19).
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 the
counter reaches the end of the count, a timer interrupt
request, 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 microprocessor clock divide-by-four, or an
external signal input through Port 3. The Timer Mode
register configures 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.
The counter/timers can be cascaded by connecting the T0
output to the input of T1. T_IN Mode is enabled by setting
R243 PRE1 Bit D1 to 0.
OSC
D1 (SMR)
÷2
D0 (SMR)
Internal Data Bus
Write
Write
Read
PRE0
Initial Value
Register
T0
Initial Value
Register
T0
Current Value
Register
÷16
6-Bit
÷4
Down
8-bit
Down
Counter
Counter
IRQ4
Internal
Clock
External Clock
÷2
TOUT
P36
Clock
Logic
÷4
6-Bit
Down
Counter
8-Bit
Down
Counter
IRQ5
Internal Clock
Gated Clock
Triggered Clock
TIN P31
PRE1
Initial Value
Register
T1
Initial Value
Register
T1
Current Value
Register
Write
Write
Read
Internal Data Bus
Figure 19. Counter/Timer Block Diagram
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