CNC | Program Name and Number Identification


A CNC program can be identified by its number and – on some controls – also by its name. Identification by the program number is necessary in order to store more than one program in the CNC memory. Program name or a brief description, if supported, can be viewed on the control screen display.

Program Number

The first block used in any part program is commonly a program number, and must be specified in the program, if the control system requires it. Two addresses are available for the program number – the capital letter O for EIA format, and the older colon [ : ] for ASCII (ISO) format. In memory operation, the control system always displays program number with the letter O. Program number block is not always necessary to include in the CNC program and often it is better to let the CNC operator make the selection.

If a program does use program numbers, they must be specified within a certain range. Programs for older Fanuc controls must be within the range of O1 – O9999, program number zero (O0 or O0000) is not allowed. Newer controls allow 5-digit program numbers, in range of O1 – O99999. Neither a decimal point or a negative sign is not allowed in any program number. Leading zeros suppression is normal – for example, O1, O01, O001, O0001, and O00001 are all legitimate entries, in this case for a program number one.

Program Name

On the latest Fanuc control systems, the program name can be included in addition to the program number, not instead of it. Program name (or a brief program description) can be up to sixteen characters long (spaces and symbols are counted). The program name must be on the same line (in the same block) as the program number:

O1001 (DWG. A-124D IT.2)

There is a distinct advantage of displaying the program number along with its description – it makes the directory listing more descriptive and useful.

Watch carefully where the description is written. If the program name is longer than sixteen characters allowed, no error is generated, but only the first sixteen characters will be displayed. Make sure to avoid program names that can be ambiguous when displayed. Consider these two program names, they both appear to be correct:


Since the control screen display can only show the first sixteen characters of program name, the program names will be ambiguous when displayed:


To eliminate this problem, use an abbreviated description that falls within the sixteen characters and still contains all significant information – for example:


If a detailed description is required, it has to be divided over one or more comment blocks:


Specified comments in the block or blocks following the program number will not appear on the directory screen listing, but still will be a useful aid to the CNC operator. They will be displayed during the program processing and, of course, listed in a hard copy printout.
Program names should be short and descriptive – their purpose is to assist the CNC operator when searching for programs stored in the control memory. Any suitable information could include a drawing number or a part number, shortened part name, operation, etc. Descriptions not suitable in such blocks include machine model, control system, programmer’s name, dates and times, company or customer’s name and similar data – they can be part of program header.

On most controls, when loading part program into the memory, CNC operator must specify the program number, regardless of what the actual number is in the program. Program number entered at the control always supercedes the programmer specified number. It can be a number that just happens to be available (unused), or it can be a number that has a unique meaning, for example, a unique group (for example, all programs that begin with the O10xx belong to the group associated with a single customer). Subprograms are different – they must always be stored using the number specified by the CNC programmer. Innovative use of program numbers may also serve to keep track of programs developed for each machine or part.