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DMx820 User’s Manual
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Count value writing during counting: It does not affect the one-shot pulse being counted until retriggering occurs.
Mode 2
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Application: Rate generator, real-time interrupt clock.
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Output operation: The output is set to “H” level by control word setting. When the initial count value is decremented to 1, t
he output is set
to “L” level during one clock pulse, and is then set to “H” level again. The initial count value is relo
aded, 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.
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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 i
s reloaded and
counting starts. The gate input can be used for counter synchronization in this way.
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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 writi
ng the initial count value N. Counter
synchronization by software is possible in this way.
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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
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Application: Baud rate generator, square wave generator
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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.
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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.
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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.
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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.
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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.
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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 oper
ations 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
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Application: Software trigger strobe
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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.
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Gate function: “H” level validates counting and “L” level invalidates counting. The gate signal does not affect the output.
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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,
