Z8
®
CPU
User Manual
UM001604-0108
Counters and Timers
83
Counter/Timer Operation
Under software control, counter/timers are started and stopped via the Timer Mode Regis-
ter (TMR,
F1h
) bits D0–D3 (see
). Each counter/timer is associated with a Load
bit and an Enable Count bit.
Load and Enable Count Bits
Setting the Load bit (D0 for T0 and D2 for T1) transfers the initial value in the prescaler
and the counter/timer registers into their respective down-counters. The next internal
clock resets bits D0 and D2 to 0, readying the Load bit for the next load operation. New
values may be loaded into the down-counters at any time. If the counter/timer is running, it
continues to do so and starts the count over with the new value. Therefore, the Load bit
actually functions as a software re-trigger.
Figure 72. Counter/Timer 0 and 1 Registers
Figure 73. Timer Mode Register
D7 D6 D5 D4 D3 D2 D1 D0
(%F4; Write/Read Only)
current value when read
Initial value when written
(Range 1-256 decimal, 01-00 HEX)
Counter/Timer 0 Register
R244 T0
(%F2; Write/Read Only)
Counter/Timer 1 Register
R242 T1
D3 D2 D1 D0
(% F1; Read/Write)
0 = Disable T
0
Count
0 = No Function
1 = Load T
0
Timer Mode Register
R241 TMR
1 = Enable T
0
Count
0 = No Function
1 = Load T
1
0 = Disable T
1
Count
1 = Enable T
1
Count
