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Z8 Microcontrollers
Counter/Timers
ZiLOG
6-6
UM001600-Z8X0599
6.4 T
OUT
MODES
(Continued)
The counter/timer to be output is selected by TMR bit 7
and bit 6. T0 is selected to drive the T
OUT
line by setting bit
7 to 0 and bit 6 to 1. Likewise, T1 is selected by setting bit
7 and bit 6 to 1 and 0, respectively. The counter/timer T
OUT
mode is turned off by setting TMR bit and bit 6 both to 0,
freeing P36 to be a data output line.
T
OUT
is initialized to a logic 1 whenever the TMR Load bit
(bit 0 for T0 or bit 1 for T2) is set to 1. The T
OUT
configura-
tion timer load, and Timer Enable Count bits for the
counter/timer driving the T
OUT
pin can be set at the same
time. For example, using the instruction:
OR TMR,#43H
Configures T0 to drive the T
OUT
pin (P36).
Sets the P36 T
OUT
pin to a logic 1 level.
Loads the initial PRE0 and T0 levels into their respective
counters and starts the counter after the M2T2
machine state after the operand is fetched.
At end-of-count, the interrupt request line (IRQ4 or IRQ5),
clocks a toggle flip-flop. The output of this flip-flop drives
the T
OUT
line, P36. In all cases, when the selected
counter/timer reaches its end-of-count, T
OUT
toggles to its
opposite state (Figure 6-11). If, for example, the
counter/timer is in Continuous Counting Mode, Tout will
have a 50 percent duty cycle output. This duty cycle can
easily be controlled by varying the initial values after each
end-of-count.
The internal clock can be selected as output instead of T0
or T1 by setting TMR bit 7 and bit 6 both to 1. The internal
clock (XTAL frequency/2) is then directly output on P36
(Figure 6-12).
While programmed as T
OUT
, P36 cannot be modified by a
write to port register P3. However, the Z8
software can
examine the P36 current output by reading the port regis-
ter.
Figure 6-11. T0 and T1 Output Through T
OUT
÷
2
P3
6
T
OUT
TMR
D
7
- D
6
= 01
IRQ
4
(T0 End-of-Count)
IRQ
5
(T1 End-of-Count)
TMR
D
7
- D
6
= 10
Figure 6-12. Internal Clock Output Through T
OUT
OSC
÷
2
P3
6
T
OUT
Internal
Clock
TMR D
6
TMR D
7