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Programming Appendix A
Basic Information on Programming
Basic Information on Instructions
Programs consist of instructions. The conceptual structure of the inputs to and outputs from an instruction is
shown in the following diagram.
Power Flow
The power flow is the input condition that is used to control the execution of instructions when programs are
executing normally. In a ladder program, power flow represents the status of the input condition.
1. Input Instructions
• Load instructions indicate a logical start and output the input condition.
• Intermediate instructions input the power flow as an input condition and output the power flow to an inter-
mediate or output instruction as an input condition.
2. Output Instructions
Output instructions execute functions, using the power flow as an input condition.
Instruction Conditions
Instruction conditions are special conditions related to overall instruction execution that are output by the
instructions listed below. Instruction conditions have a higher priority than the input condition when it comes to
deciding whether or not to execute an instruction. An instruction may not be executed or may act differently
depending on instruction conditions. Instruction conditions are reset (canceled) at the start of each task, i.e.,
they are reset when the task changes.
Flags
Instruction
Flag
Input condition
Instruction conditions
Input condition
*
1
Instruction conditions
*
2
Operands
(sources)
Operands
(destinations)
Memory
*1: Input instructions only.
*2: Not output for all instructions.
Outputs the input condition.
=
D00000
#1215
Outputs the input condition.
Input block Output block
Input condition for
output instruction
Input condition for LD