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¡ Semiconductor

MSM82C54-2RS/GS/JS

Mode 2

• Application: Rate generator, real-time interrupt clock.

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

count value is decremented to 1, the output is set to “L” level during one clock pulse, and is

then set to “H” level again. The initial count value is reloaded, and the above sequence

repeats. In mode 2, the same sequence is repeated at intervals of N clock pulses if the initial

count value is N for example.

• Gate function: “H” level validates counting, and “L” level invalidates it. If the gate signal is

set to “L” level when the output pulse is “L” level, the output is immediately set to “H” level.

At the falling edge of the clock pulse succeeding the trigger, the count value is reloaded and

counting starts. The gate input can be used for counter synchronization in this way.

• Count value load timing:

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

at the falling edge of the next clock pulse. The output is set to “L” level upon lapse of N clock

pulses after writing the initial count value N. Counter synchronization By software is possible

in this way.

• Count value writing during counting:

Count value writing does not affect the current counting operation sequence. If new count

value writing completes and the gate trigger arrives before the end of current counting

operation, the count value is loaded to the CE at the falling edge of next clock pulse and

counting continues from the new count value. If no gate trigger arrives, the new count value

is loaded to the CE at the end of the current counting operation cycle. In mode 2, count value

of 1 is prohibited.

Mode 3

• Application: Baud rate generator, square wave generator

• Output operation: Same as mode 2 except that the output duty is different.

The output is set to “H” level by control word setting. When the count becomes half the initial

count value, the output is set to “L” level and kept at “L” level during the remainder of the

count. Mode 3 repeats the above sequence periodically. If the initial count value is N, the

output becomes a square wave with a period of N.

• Gate operation: “H” level validates counting, and “L” level invalidates it. If the gate signal

is set to “L” level when the output is “L” level, the output is immediately set to “H” level. The

initial count value is reloaded at the falling edge of the clock pulse succeeding the next gate

trigger. The gate can be used for counter synchronization in this way.

• 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, Counter synchronization by software is possible

in this way.

• Count value writing during counting:

The count value writing does not affect the current counting operation. When the gate trigger

input arrives before the end of a half cycle of the square wave after writing the new count

value, the new count value is loaded in the CE at the falling edge of the next clock pulse, and

counting continues using the new count value. If there is no gate trigger, the new count value

is loaded at the end of the half cycle and counting continues.

• Even number counting operation:

The output is initially set to “H” level. The initial count value is loaded to the CE at the falling

edge of the next clock pulse, and is decremented by 2 by consecutive clock pulses. When the

counter value becomes 2, the output is set to “L” level, the initial value is reloaded and then

the above operation is repeated.