11/19

¡ Semiconductor

MSM82C53-2RS/GS/JS

Mode Definition

• Mode 0 (terminal count)

The counter output is set to “L” level by the mode setting. If the count value is then written

in the counter with the gate input at “H” level (that is, upon completion of writing the MSB

when there are two bytes), the clock input counting is started. When the terminal count is

reached, the output is switched to “H” level and is maintained in this status until the control

word and count value are set again.

Counting is interrupted if the gate input is switched to “L” level, and restarted when switched

back to “H” level.

When Count Values are written during counting, the operation is as follows:

1-byte Read/Load. ............ When the new count value is written, counting is stopped

immediately, and then restarted at the new count value by the next

clock.

2-byte Read/Load ............. When byte 1 (LSB) of the new count value is written, counting is

stopped immediately. Counting is restarted at the new count

value when byte 2 (MSB) is written.

• Mode 1 (programmable one-shot)

The counter output is switched to “H” level by the mode setting. Note that in this mode,

counting is not started if only the count value is written. Since counting has to be started in

this mode by using the leading edge of the gate input as a trigger, the counter output is

switched to “L” level by the next clock after the gate input trigger. This “L” level status is

maintained during the set count value, and is switched back to “H” level when the terminal

count is reached.

Once counting has been started, there is no interruption until the terminal count is reached,

even if the gate input is switched to “L” level in the meantime. And although counting

continues even if a new count value is written during the counting, counting is started at the

new count value if another trigger is applied by the gate input.

• Mode 2 (rate generator)

The counter output is switched to “H” level by the mode setting. When the gate input is at

“H” level, counting is started by the next clock after the count value has been written. And

if the gate input is at “L” level, counting is started by using the rising edge of the gate input

as a trigger after the count value has been set.

An “L” level output pulse appears at the counter output during a single clock duration once

every n clock inputs where n is the set count value. If a new count value is written during

while counting is in progress, counting is started at the new count value following output of

the pulse currently being counted. And if the gate input is switched to “L” level during

counting, the counter output is forced to switch to “H” level, the counting being restarted by

the rising edge of the gate input.

• Mode 3 (square waveform rate generator)

The counter output is switched to “H” level by the mode setting. Counting is started in the

same way as described for mode 2 above.

The repeated square wave output appearing at the counter output contains half the number

of counts as the set count value. If the set count value (n) is an odd number, the repeated square

wave output consists of only (n+1)/2 clock inputs at “H” level and (n-1)/2 clock inputs at “L”

level.

If a new count value is written during counting, the new count value is reflected immediately

after the change (“H” to “L” or “L” to “H”) in the next counter output to be executed. The

counting operation at the gate input is done the same as in mode 2.