PLC technical terms – Glossary

Address – The location in a PLC memory where particular information is stored. Can be always used a specific I/O rack, module, and terminal location.

Analog input/output – An input or output circuit that uses an analog-to-digital converter to
translate a continuous analog signal into digital and vice versa

ASCII – American Standard Code for Information Interchange. A seven-bit code
with an optional parity bit used to represent alphanumeric, punctuation, and
control characters.

BCD – binary coded decimal . A binary number system in which each decimal digit
from 0 to 9 is represented by four binary digits (bits). The four positions have a
weighted value of 1, 2, 4, and 8, respectively, starting from the least significant
bit.

Bit – binary digit. The smallest unit of binary information. A bit can have a value
of 1 or 0.

Byte – A group of eight bits that are operated on as a unit, such as when
moving data to or from memory.

CPU – central processing unit. The part of a programmable controller responsible
for reading inputs, executing the control program, and updating outputs.

Chassis – A hardware assembly that houses PLC devices, such as I/O modules.

HMI (Human-Machine Interface) – The interface between an operator and a PLC system, often a touchscreen or monitor.

Ladder Logic – A graphical programming language used to program PLCs, resembling relay logic diagrams.

PLC – programmable logic controller – control device that can be programmed to control process or machine operations.

Rung– A horizontal line in ladder logic programming representing a logical operation.

Scan time – The time required to complete process of reading all inputs, executing the control program, and updating all outputs.