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11 Use of High-speed Counters
11.6 Timing of Updating of Current Value and Comparison of Current Value
166
FX3G Series Programmable Controllers
User's Manual - Hardware Edition
11.6 Timing of Updating of Current Value and Comparison of Current Value
11.6.1 Timing of updating of current value
When pulses are input to an input terminal for a high-speed counter, the high-speed counter executes up-
counting or down-counting. The current values of devices are updated when counting is input.
11.6.2 Comparison of current value
To compare and output the current value of a high-speed counter, the following two methods are available.
1. Use of comparison instruction (CMP), band comparison instruction (ZCP) or contact
comparison instruction
Use the comparison instruction (CMP), band comparison instruction (ZCP) or contact comparison instruction
if the comparison result is necessary at counting. Use these instructions only when high-speed processing is
not required because these instructions are processed in the operation cycle of the PLC, and operation delay
is generated before the comparison output result is obtained. Use the comparison instructions for high-speed
counters (HSCS, HSCR and HSZ) described below if it is necessary to execute comparison and change the
output contact (Y) at the same time when the current values of high-speed counters change.
2. Use of Comparison instruction for high-speed counters (HSCS/HSCR/HSZ instruction)
Comparison instructions for high-speed counters (HSCS, HSCR and HSZ instructions) perform comparison
and output the comparison results with the relevant high-speed counting operation. These instructions have
limitations on the number of simultaneously driven instructions as shown in the following table.
When the output relay (Y) has been designated for comparison results, the ON/OFF status of the output is
affected directly until the END instruction output is refreshed.
When the PLC is a relay output type, a mechanical delay in operation (approx. 10ms) is caused.
Therefore, it is best to use a transistor output type PLC.
*1. The overall frequency changes when the HSCS, HSCR or HSZ instruction is used.
→ For details on the overall frequency, refer to Section 11.7.
Applied instruction Limitation in number of instructions driven at same time
HSCS
*1
6 instructions
HSCR
*1
HSZ
*1