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¡ Semiconductor

MSM82C54-2RS/GS/JS

Mode definition

Mode 0

• Application: Event counter

• Output operation: The output is set to “L” level by the control word setting, and kept at “L”

level until the counter value becomes 0.

• Gate function: “H” level validates the count operation, and “L” level invalidates it. The gate

does not affect the output.

• Count value load timing: after the control word and initial count value are written, the count

value is loaded to the CE at the falling edge of the next clock pulse. The first clock pulse does

not cause the count value to be decremented. In other words, if the initial count value is N,

the output is not set to “H” level until the input of (N+1) the clock pulse after the initial count

value writing.

• Count value writing during counting:

The count value is loaded in the CE at the falling edge of the next clock, and counting with the

new count value continues. The operation for 2-byte count is as follows:

1) The counting operation is suspended when the first byte is written. The output is

immediately set to “L” level. (no clock pulse is required.)

2) After the second byte is written, the new count value is loaded to the CE at the falling edge

of the next clock.

For the output to go to “H” level again, N+1 clock pulse are necessary after new count value

N is written.

• Count value writing when the gate signal is “L” level:

The count value is also loaded to the CE at the falling edge of the next clock pulse in this case.

When the gate signal is set to “H” level, the output is set to “H” level after the lapse of N clock

pulses. Since the count value is already loaded in the CE, no clock pulse for loading in the CE

is necessary.

Mode 1

• Application: Digital one-shot

• Output operation: The output is set to “H” level by the control word setting. It is set to “L”

level at the falling edge of the clock succeeding the gate trigger, and kept at “L” level until the

counter value becomes 0. Once the output is set to “H” level, it is kept at “H” level until the

clock pulse succeeding the next trigger pulse.

• Count value load timing:

After the control word and initial count value are written, the count value is loaded to the CE

at the falling edge of the clock pulse succeeding the gate trigger and set the output to “L” level.

The one-shot pulse starts in this way. If the initial count value is N, the one-shot pulse interval

equals N clock pulses. The one-shot pulse is not repetitive.

• Gate function: The gate signal setting to “L” level after the gate trigger does not affect the

output. When it is set to “H” level again from “L” level, gate retriggering occurs, the CR count

value is loaded again, and counting continues.

• Count value writing during counting

It does not affect the one-shot pulse being counted until retriggering occurs.