December 2013

Basic Programming Terms – CNC Structure in 4 Steps

CNC program structure progresses through four levels: character, word, block, and program.

1. Character

A character is the smallest unit in CNC programming. It may be a letter, digit, or symbol. Letters identify commands or data types, digits form numerical values, and symbols provide notation such as decimal points, parentheses, minus signs, and percent signs. Exact symbol support depends on the machine control.

2. Word

A word combines characters, typically a capital letter followed by a numerical value. Words communicate individual pieces of information such as spindle speed, feed rate, position, or machine functions.

3. Block

A block, sometimes called a sequence block, contains one or more words that together form a complete command or machining step. Each block is written on a separate line and terminated by an end-of-block code.

4. Program

A CNC program is an ordered collection of blocks used to machine a part. It generally begins with a program number, proceeds through blocks arranged in operational sequence, and ends with an appropriate stop or cancellation command.

Character → Word → Block → Program