Mitsubishi Electric MELSEC FX3U Programming Manual page 371

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
4. Caution on the counting operation when the current value is changed
An instruction for the high speed counter gives the comparison result when a pulse is input to the input (X) of
the high speed counter.
However, the comparison result is not given when the current value of the high speed counter is changed in
the following method:
1) Change method (examples)
a) Overwriting the contents of a word device used as the comparison value using DMOV instruction, etc.
b) Resetting the current value of a high speed counter in a program
2) Operation
Even if the condition for setting the output to ON or OFF is given as the comparison result, the
comparison result does not change when an instruction is simply driven.
5. Reset operation by an external terminal [M8025
For a high speed counter equipped with an external reset terminal (R) such as C241, an instruction is
executed and the comparison result is output at the rising edge of the reset input signal.
In FX PLCs, high speed counters operate in the HSC (external reset) mode without regard to the status of
3G
M8025.
1) Program
If an instruction for the high speed counter is used while M8025
again when the current value of the high speed counter C241 is cleared by an external reset terminal.
And the comparison result is output even if a counting input is not given.
M8000
RUN monitor
*1. M8025 is cleared when the PLC mode is changed from RUN to STOP.
It is not necessary to drive M8025 in FX
2) Operation
When the external reset input X001 turns ON while the current value of C241 is "100", for example, the
current value of C241 is reset to "0". And Y000 is reset at this time even if a counting input is not given.
M8025 *1 External reset mode
X001
K9,999
C241
FNC 54
K 0 C241
DHSCR
3G
13 High Speed Processing – FNC 50 to FNC 59
13.4 FNC 53 – HSCS / High Speed Counter Set
*1
: HSC (external reset) mode]
*1
is driven, the instruction is executed
External reset
terminal for C241
Y000
PLCs.
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