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Reload counter operation, Counter activation and operation timing – FUJITSU MB91460 SERIES FR60 User Manual

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Chapter 40 Pulse Frequency Modulator

3.Reload Counter Operation

3. Reload Counter Operation

This section describes the operations of the 16-bit reload counter: Internal clock operation and
Underflow operation

Internal Clock Operation

The machine clock divided by 2, 8, 32, 64 or 128 can be selected as the clock source when
operating the counter from an internal clock.

Writing "1" to both the CNTE and TRG bits in the control status register enables and starts
counting simultaneously.

Using the TRG bit as a trigger input is always available when the counter is enabled (CNTE =
"1"), regardless of the operation mode.

Figure 3-1 shows counter activation and counter operation.

A time f (f: peripheral clock machine cycle) is required from the counter start trigger being input
until the reload register data is loaded into counter.

Counter activation and operation timing

Figure 3-1 Counter Activation and Operation Timing

Underflow Operation

An underflow occurs when the counter value changes from 0000

H

to FFFF

H

. Therefore, an

underflow occurs after "reload register setting + 1" counts.

If the RELD bit in the control register is "1" when the underflow occurs, the contents of the reload
register are loaded into the counter and counting continues. When RELD is "0", counting stops
with the counter at FFFF

H

.

The UF bit in the control register is set when the underflow occurs. If the INTE bit is "1" at this
time, an interrupt request is generated.

Figure 3-2 shows the operation when an underflow occurs.

Count clock

TRG (register)

Counter

CNTE (register)

Data load

Reload data

–1

–1

–1

φ