Z86D99 ZILOG [Zilog, Inc.], Z86D99 Datasheet - Page 46

• Manufacturer Part Number: Z86D99
• Description: Low-Voltage Micro controllers with ADC
• Manufacturer: ZILOG [Zilog, Inc.]

PS003807-1002
Figure 24. Counting Modes
When the PRE
prescaler divides by 64. If that number is 000001, the prescaler does not divide
and passes its clock on to T
Each time the prescaler reaches its end-of-count, a carry is generated, which
allows the counter/timer to decrement by one on the next timer clock input. When
T
IRQ
comes to rest with its value at
matically reloaded and counting continues (continuous mode). In single-pass
mode, the prescaler still continues to decrement when the timer T
its end-of-count. The prescaler always starts from its programmed value upon
restarting the counter.
The counting modes are controlled by bit D
gle-pass counting mode or set to
The counter/timer can be stopped at any time by setting the Enable Count bit to
and restarted by setting the Enable Count bit back to
tinues its count value at the time it was stopped. The current value in the T
counter/timer can be read at any time without affecting the counting operation.
New initial values can be written to the prescaler or the counter/timer registers at
any time. These values are transferred to their respective down-counters on the
next load operation. If the counter/timer mode is continuous, the next load occurs
on the timer clock following an end-of-count. New initial values must be written
before the load operation because the prescaler always effectively operates in
continuous count mode.
If the value loaded in the T
counting at all; the timer is passing the prescaler end-of-count through. Because
the prescaler is continuously running, regardless of the single-pass/continuous
mode operation, the 8-bit timer continuously times out at the rate of the prescaler
end-of-count if the T
1
and PRE
5
for T
1
. Depending on the counting mode selected, the counter/timer either
1
both reach their end-of-count, an interrupt request is generated—
1
register is loaded with 000000 in the six most significant bits, the
P
1
timer value is programmed to
R
E
1
1
register is
.
L
Prescaler 1 Register
00h
(
I
F3h
1
(single-pass mode), or the initial value is auto-
R243 PRE1
M
for continuous mode.
; Read/Write)
Z86D990/Z86D991 OTP and Z86L99X ROM
D
0
01h
I
Low-Voltage Microcontrollers with ADC
N
, the timer is actually not timing or
0
of PRE
A
Count mode
1 = T
0 = T
R
1
1
01h
1
Y
modulo-N
single pass
, with D
1
. The T
.
0
1
cleared to
counter/timer con-
1
has reached
0
1
for sin-
0
39