Circuits Not Available In Structured Ladder Programs And Countermeasures; Handling Of General Flags - Mitsubishi Electric MELSEC FX Series Structured Programming Manual

FXCPU Structured Programming Manual
(Application Functions)
1.3.3

Circuits not available in structured ladder programs and countermeasures

1. Bridge circuit
A circuit in which the current flows in both directions should be changed as shown in the right figure (so that a
circuit without D and a circuit without B are connected in parallel).
A B
E
C
D
2. Coil connection position
• You can program a contact on the right side of a coil. In this case, make sure to program a coil (including a
function or function block) at the end of the circuit.
A
1.3.4

Handling of general flags

The following flags are valid in general sequence instructions:
(Examples)
M8020:Zero flag
M8029:Instruction execution complete flag
M8328:Instruction non-execution flag
M8304:Zero flag
*1. Supported only in FX
*2. Supported only in FX
Each of these flags turns ON or OFF every time the PLC executes a corresponding instruction. These flags
do not turn ON or OFF when the PLC does not execute a corresponding instruction or when an error occurs.
Because these flags are related to many sequence instructions, their ON/OFF status changes every time the
PLC executes each corresponding instruction.
Refer to examples in the next page, and program a flag contact just under the target sequence instruction.
18
F
C
B D
E
M8021:Borrow flag
*1
*1
M8306:Carry flag
/FX PLCs.
3U 3UC
/FX /FX
3U 3UC
1.3 Cautions on Creation of Fundamental Programs
C E
A
A E
C
A
Or
A E
M8022:Carry flag
M8090:Block comparison signal
M8329:Instruction execution abnormal complete flag
*1
PLCs.
3G
F
B
D
E
B D C
B D C
*1
1 Outline
*2