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FX
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Series Programmable Controllers
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3UC
Programming Manual - Basic & Applied Instruction Edition
4.7.9
Conditions for hardware counters to be handled as software counters
High speed counters are classified into hardware counters and software counters. In some conditions,
however, hardware counters are handled as software counters.
In this case, use hardware counters within the range of maximum response frequency and total frequency as
determined for software counters.
Conditions under which counters are handled as software counters
Hardware
counter No.
C235
C236
C237
C238
C239
C240
C244(OP)
C245(OP)
C246
C248(OP)
C251
C253
118
Condition in which hardware counters are handled as software counters
Because hardware counters execute counting at the hardware level of the FX
execute counting regardless of the total frequency.
However, when hardware counters are handled as software counters with the following conditions, their
maximum response frequency and total frequency are limited in the same way as the software counters.
Use M8380 to M8387 to check whether high speed counters are handled as hardware counters or
software counters.
• When DHSCS (FNC 53), DHSCR (FNC 54), DHSZ (FNC 55) or DHSCT (FNC280) instruction is used
for a hardware counter number, the hardware counter is handled as a software counter.
Example: C235
DHSCS
In this case, C235 is handled as a software counter.
• When an index register is used for a counter number specified in DHSCS (FNC 53), DHSCR
(FNC 54), DHSZ (FNC 55) or DHSCT (FNC280) instruction, all hardware counters are handled as
software counters.
Example: C235Z0
DHSCS
• C253 (hardware counter) is handled as a software counter by inverting the logic using the external
reset input signal logic changing function.
Example: The logic of the C253 external reset input signal is inverted.
→For logic inversion of the external reset input signal, refer to Subsection 4.7.6.
M8388
4.7 High Speed Counter [C] (FX3U/FX3UC PLC)
C235
K
K100 C235 Y000
K100
Y000
C235Z0
M8389
C253
K
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