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¡ Semiconductor

MSM82C54-2RS/GS/JS

• Odd number counting operation:

The output is initially set to “H” level. At the falling edge of the next clock pulse, the initial

count value minus one is loaded in the CE, and then the value is decremented by 2 by

consecutive clock pulses. When the counter value becomes 0, the output is set to “L” level,

and then the initial count value minus 1 is reloaded to the CE. The value is then decremented

by 2 by consecutive clock pulses. When the counter value becomes 2, the output is again set

to “H” level and the initial count value minus 1 is again reloaded. The above operations are

repeated. In other words, the output is set to “H” level during (N+1)/2 counting and to “L”

level during (N-1)/2 counting in the case of odd number counting.

Mode 4

• Application: Software trigger strobe

• Output operation: The output is initially set to “H” level. When the counter value becomes

0, the output goes to “L” level during one clock pulse, and then restores “H” level again.

The count sequence starts when the initial count value is written.

• Gate function: “H” level validates counting, and “L” level invalidates counting. The gate

signal 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 clock pulse does not decrement the initial count

value. If the initial count value is N, the strobe is not output unless N+1 clock pulses are input

after the initial count value is written,

• Count value writing during counting:

The new count value is written to the CE at the falling edge of the next clock pulse, and

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

1) First byte writing does not affect the counting operation.

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

of the next clock pulse.

This means that the counting operation is retriggered by software. The output strobe is set to

“L” level upon input of N+1 clock pulses after the new count value N is written.

Mode 5

• Application: Hardware trigger strobe

• Output operation:

The output is initially set to “H” level. When the counter value becomes 0 after triggering by

the rising edge of the gate pulse, the output goes to “L” level during one clock pulse, and then

restores “H” level.

• Count value load timing:

Even after the control word and initial count value are written, loading to the CE does not

occur until the input of the clock pulse succeeding the trigger. For the clock pulse for CE

loading, the count value is not decremented. If the initial count value is N, therefore, the

output is not set to “L” level until N+1 clock pulses are input after triggering.

• Gate function:

The initial count value is loaded to the CE at the falling edge of the clock pulse succeeding gate

triggering. The count sequence can be retriggered.

The gate pulse does not affect the output.