Z86L99X 查看數據表（PDF） - Zilog

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Z86L99X

Low-Voltage Microcontrollers with ADC

Zilog 

Z86D990/Z86D991 OTP and Z86L99X ROM

Low-Voltage Microcontrollers with ADC

39

R243 PRE1

Prescaler 1 Register

(F3h; Read/Write)

D0

Figure 24. Counting Modes

Count mode

1 = T1 modulo-N

0 = T1 single pass

When the PRE1 register is loaded with 000000 in the six most significant bits, the

prescaler divides by 64. If that number is 000001, the prescaler does not divide

and passes its clock on to T1.

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

T1 and PRE1 both reach their end-of-count, an interrupt request is generated—

IRQ5 for T1. Depending on the counting mode selected, the counter/timer either

comes to rest with its value at 00h (single-pass mode), or the initial value is auto-

matically reloaded and counting continues (continuous mode). In single-pass

mode, the prescaler still continues to decrement when the timer T1 has reached

its end-of-count. The prescaler always starts from its programmed value upon

restarting the counter.

The counting modes are controlled by bit D0 of PRE1, with D0 cleared to 0 for sin-

gle-pass counting mode or set to 1 for continuous mode.

The counter/timer can be stopped at any time by setting the Enable Count bit to 0

and restarted by setting the Enable Count bit back to 1. The T1 counter/timer con-

tinues its count value at the time it was stopped. The current value in the T1

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 T1 register is 01h, the timer is actually not timing or

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 T1 timer value is programmed to 01h.

PS003807-1002

PRELIMINARY

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