Understanding DPRNT in Fanuc Macro Programming

The DPRNT command is widely used in Fanuc Macro B programming to output data from a CNC machine to an external device such as a computer, printer, or monitoring system. It allows programmers to record machining data, offsets, or inspection results directly from the control. When used correctly, DPRNT becomes a powerful tool for process monitoring, quality control, and automated data logging in CNC machining.

Character Rules

DPRNT allows you to use formatted data consisting of both text and arbitrary variables. The text portion can contain uppercase letters (A-Z), numbers (0–9), and a limited set of special characters such as +, −, /, *, ., etc. Variables cannot be used as aliases: SETVN or in indexable form:
#[<value>]

An asterisk (*) represents a space. This is commonly used to structure readable output lines.

Basic Structure

DPRNT commands typically operate within an output session that begins with POPEN and ends with PCLOS.

POPEN DPRNT [] PCLOS

POPEN - opens the communication channel.
DPRNT [] - can contain formatted text and variables, as well as be empty, which will be displayed as a new line
PCLOS - closes the output channel.

Everything inside the brackets is transmitted through the CNC control’s output interface.

Formatting Macro Variables

Variables can be formatted using the structure:

#100[ab]

Where:

a - specifies the number of digits before the decimal point
b - specifies the number of digits after the decimal point

For example:

#100[33]

This prints the value of variable #100 with three digits before and three digits after the decimal point.

Important

Fanuc, Haas and Mazak controls limit variable output to a maximum of eight digits in total (a+b less or equal 8).

Handling Null Variables

Different Fanuc controls treat null variables differently.

Fanuc 6 – Null variables cannot be printed and will trigger Alarm #114.
Fanuc 10/11/15/16/18/21 – Null variables are automatically printed as 0.
Haas – Null variables are automatically printed as 0.

Good to know

Because of these differences, programmers working with older controls should validate variables before printing.

Practical Example

The following code outputs all work offsets from G54 to G59:

Why DPRNT Is Useful

DPRNT is commonly used in CNC environments for:

Automatic offset reporting
SPC and quality data collection
Recording probing results
Logging tool or process data
Integrating machines with external monitoring systems

For advanced CNC macro users, DPRNT provides a simple but effective way to connect machining processes with digital data tracking.