Mitsubishi Electric MELSEC FX3U - Page 378

376
FX3G/FX3U/FX3UC Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
13 High Speed Processing – FNC 50 to FNC 59
13.6 FNC 55 – HSZ / High Speed Counter Zone Compare
Cautions
1. Selection of the count comparison method
1) FX3U/FX3UC PLC
When the HSZ instruction is used in FX
3U/FX3UC PLCs, hardware counters (C235, C236, C237, C238,
C239, C240, C244 (OP), C245 (OP), C246, C248 (OP), C251 and C253) are automatically switched to
software counters, and the maximum frequency and total frequency of each counter are affected.
Refer to the counting operation described below, and select according to the contents of control whether
to use DHSZ instruction or general-purpose comparison instruction.
a) Case to select DHSZ instruction
- When the output should be given when the counting result becomes equivalent to the comparison
value regardless of the scan time of the PLC
b) Cases to select a general-purpose comparison instruction
- When the frequency is beyond the counting performance of software counters (and below the
counting performance of hardware counters)
- When counting is important, but the effect of the scan time can be ignored in operations depending
on the counting result
- When the number in an instruction is more than 32
2) FX
3G PLCs
When the HSZ instruction is used in FX
3G PLCs, the total frequency of each counter is affected.
Refer to the counting operation described below, and select according to the contents of control whether
to use the HSZ instruction or a general-purpose comparison instruction.
a) Case to select the HSZ instruction
- When the output should be given if the counting result becomes equivalent to the comparison
value without regard to the scan time of the PLC
b) Cases to select a general-purpose comparison instruction
- When counting is regarded as important, but the effect of the scan time can be ignored in
operations according to the counting result
- When an instruction is used 6 times or more
M8000
DHCMOV
C251 D100
Y010
K0
Y011
Y012
FNC225
LDD >
K10000 D100
FNC229
LDD <=
K10000 D100
FNC238
ANDD >=
K20000 D100
FNC226
LDD <
K20000 D100
M8000
FNC 50
REF
Y010 K8
M8000
Y010 K8
FNC 50
REF
FNC229
LDD<=
FNC225
LDD>
FNC226
LDD<
FNC238
ANDD>=
K10000
K10000
K20000
K20000
C251
C251
C251
C251
Y012
Y011
Y010