Mitsubishi Electric MELSEC FX3U Programming Manual page 378

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
Cautions
1. Selection of the count comparison method
1) FX /FX
3U 3UC
When the HSZ instruction is used in FX
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
M8000
FNC225
LDD >
FNC229
LDD <= K10000
FNC226
LDD <
M8000
2) FX PLCs
3G
When the HSZ instruction is used in FX
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
FNC225
LDD>
FNC229
LDD<=
FNC226
LDD<
M8000
376
PLC
DHCMOV
K10000 D100
FNC238
D100 ANDD >= K20000
K20000 D100
K10000 C251
FNC238
K10000 C251
ANDD>=
K20000 C251
13 High Speed Processing – FNC 50 to FNC 59
13.6 FNC 55 – HSZ / High Speed Counter Zone Compare
/FX PLCs, hardware counters (C235, C236, C237, C238,
3U 3UC
C251 D100 K0
Y010
D100
Y011
Y012
FNC 50
Y010 K8
REF
PLCs, the total frequency of each counter is affected.
3G
Y010
K20000 C251
Y011
Y012
FNC 50
Y010 K8
REF