Instruction list is a programming language designed for PLC, supported by the IEC 61131-3 standard. The instruction list consists of a series of instructions. Each instruction begins on a new line, contains - an Operator, if necessary with a Modifier and if necessary one or more Operands
Instruction list language is a low-level language, will execute much faster in PLC than graphical languages like ladder logic programming. This language is also more compact and needs less space in PLC memory.
Instruction list - Basic instructions:
Load instruction:
LD: Open contact: contact is active (result is 1), while the control bit is 1.
LDN: Close contact: contact is active (result is 1), while the control bit is 0.
LDR: Contact in the rising edge: contact is active during a scan cycle, where the control bit has a rising edge.
LDF: Contact in the falling edge: contact is active during a scan cycle, where the control bit has a falling edge.
Store instruction:
ST: The result of the logic function activates the coil.
STN: The inverse result of the logic function activates the coil.
S: The result of the logic function energizes the relay (sets the latch).
R: The result of the logic function de-energizes the relay (resets the latch).
OR instruction:
OR: OR of the operand with the result of the previous logical operation.
ORN: OR of the operand with the inverted result of the previous logical operation.
ORR: OR of the rising edge with the result of the previous logical operation.
ORF: OR of the falling edge with the result of the previous logical operation.