Cautions On Use - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition

4.7.11 Cautions on use

• For a contact to drive the coil of a high speed counter, use a contact which is normally ON during high
speed counting.
Example: M8000 (RUN monitor NO contact)
Program a contact which is
normally ON during counting.
• If the operation of a high speed counter is triggered by a device such as a switch, the counter may
malfunction due to extra noise from switch chattering or contact bounce.
• The input filter of an input terminal for a high speed counter in the main unit is automatically set to 5 µs
(X000 to X005) or 50 µs (X006 and X007).
Accordingly, it is not necessary to use the REFF instruction or special data register D8020 (input filter
adjustment).
The input filter for input relays not being used for high speed counters remains at 10 ms (initial value).
• The inputs X000 to X007 are used for high speed counters, input interrupt, pulse catch, SPD/DSZR/DVIT/
ZRN instructions and general-purpose inputs. There should be no overlap between each input number.
For example, when C251 is used, X000 and X001 are occupied. As a result, "C235, C236, C241, C244,
C246, C247, C249, C252 and C254", "input interrupt pointers I00* and I10*", "pulse catch contacts M8170
and M8171" and "SPD instruction using X000 and/or X001" cannot be used.
• When a counting pulse is not provided, none of the high speed counter output contacts will turn ON, even
if the PLC executes an instruction where "present value = set value."
• Counting may be started or stopped for a high speed counter when the output coil (OUT C***) is set to ON
or OFF. Program this output coil in the main routine. If the output coil is programmed in a step ladder
(SFC) circuit, subroutine or interrupt routine, counting cannot be started or stopped until the step ladder or
routine is executed.
• Make sure that the signal speed for high speed counters does not exceed the response frequency
described above. If an input signal exceeds the response frequency, a WDT error may occur, or
communication functions such as a parallel link may malfunction.
• When a high speed counter is reset by the RST instruction, it cannot count until the RST instruction is set
to OFF.
1) Program example
X010
2) Timing chart
X000
Current
value of C235
X010
RST
C235
C235
RST C235
C235 is reset while X010 turns ON.
The current value does not change
even if pulses are input because the
3
C235 reset instruction is valid.
2
1
C235 remains reset
"RST C235" is set to ON
because the contact turns ON.
4.7 High Speed Counter [C] (FX3U/FX3UC PLC)
Input number corresponding to
C235
X000
C235
If a number of input relay for counting is specified, high
speed counter cannot execute accurate counting.
1
"RST C235" is set to OFF
because the contact turns OFF.
4 Devices in Detail
3
2
121
1
2
3
4
5
6
7
8
9
10