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1.3 Cautions on Creation of Fundamental Programs
FXCPU Structured Programming Manual
[Basic & Applied Instruction]
1.3.3 Circuits which cannot be created by 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 figure on the right (so
that a circuit without D and a circuit without B are connected in parallel).
2. Coil connection position
• You can program a contact on the right side of a coil. In this case, be sure to program a coil (including a
function or a function block) at the end of the circuit.
1.3.4 Handling of general flags
In some types of sequence instructions, the following flags operate:
<Examples> M8020: Zero flag M8021: Borrow flag
M8022: Carry flag M8029: Instruction execution complete flag
M8090: Block comparison signal
*1
M8328: Instruction non-execution flag
*1
M8329: Instruction execution abnormal complete flag
*2
M8304: Zero flag
*2
M8306: Carry flag
*2
*1. Supported only by FX3U and FX3UC PLCs.
*2. Supported only by FX
3S, FX3G, FX3GC, FX3U and FX3UC PLCs.
Each of these flags turns ON or OFF every time the PLC executes a corresponding function. These flags do
not turn ON or OFF when the PLC does not execute a corresponding function or when an error occurs.
Because these flags turn ON or OFF in many sequence instructions, the ON/OFF status of flags changes
every time such instructions are executed.
Refer to the examples in the next page, and program a flag contact just under the target sequence instruction.
A B
C
E
D
C E
A
B
A E
C
D
F F
Or
A B D A
B D
C
E
CE
AB
E
D
C