Guide for Manual Conversion of RS-274-D (Tango PCB) to RS-274-X Gerber Format

This guide provides detailed technical instructions for converting legacy RS-274-D (Standard Gerber) files generated in Tango PCB into modern, standardized RS-274-X (Extended Gerber) format. The guide covers theoretical foundations, dimension conversion procedures, shape mapping, syntax rules, as well as concrete examples of aperture reports and raw RS-274-D files.

1. Introduction: Difference Between RS-274-D and RS-274-X Formats

The primary challenge when working with legacy CAD software such as Tango PCB lies in how printed circuit board (PCB) geometry data is stored:

• RS-274-D (Standard Gerber): Contains strictly vector commands for photoplotter head positioning (e.g., X0100Y0200D01*) and tool/aperture ID calls (e.g., D10*). The Gerber file itself does not contain information regarding the shape or dimensions of aperture D10. That data resides in a separate text report (the Aperture Report, typically with a .REP or .APT extension).
• RS-274-X (Extended Gerber): A self-contained format that includes full definitions of shapes, dimensions, and measurement units for all D-codes used in the documentation at the very beginning (header) of the file. Modern CAM manufacturing software and modern Gerber viewers exclusively require the RS-274-X format.

2. Structure of Tango Aperture Report (.REP / .APT)

When generating photoplotter files in Tango PCB, the program creates a textual aperture table. The main parameters in this table are:

1. Code (D-Code): The aperture identifier, starting from D10 upwards.
2. Shape: Defines the geometry (Ellipse, Rd Rect, Rect, Square).
3. X and Y Dimensions: Physical tool size. In Tango PCB, these values are always expressed in mils (thousandths of an inch: 100 mil = 0.100 in = 2.54 mm).
4. Assignments: Section showing which D-codes are assigned to which PCB layer (routes, pads, silkscreen, mask).

Sample APT (.REP) File Example:

3. Structure of Legacy RS-274-D Gerber File

A raw RS-274-D Gerber file contains coordinate moves and light beam commands for photo-plotters:

• G70*: Sets coordinates to inches.
• G90*: Enables absolute positioning.
• G01*: Linear interpolation.
• D02*: Light beam OFF (move without drawing / Pen Up).
• D01*: Light beam ON (drawing line / Pen Down).
• D10*, D12*...: Aperture selection command.

Sample Legacy RS-274-D Gerber File Snippet:

*%FSLAX44Y44*
SFA1.0B1.0*%
G70*
G90*
G01*
D02*
D10*
X13720Y43920D02*
X13720Y43920D01*
X13720Y46870D01*
X13760Y46870D01*
X13760Y43920D01*
...
D02*
D12*
X68250Y39000D02*
X68500Y39000D01*
D02*
D10*
X68500Y39000D02*
X68500Y39000D01*
X68500Y39500D01*
X68450Y39500D01*

4. RS-274-X Header Syntax and Rules

To convert an RS-274-D file into RS-274-X, an aperture header block must be prepended to the very beginning of the file. Each aperture definition command is enclosed within percent signs (%) and terminated with an asterisk (*).

4.1. Defining Units of Measurement

The initial header line establishes the measurement system for the entire file. For inches, the command is: %MOIN*%

4.2. Shape Mapping and Conversion Formulas

Each individual aperture is defined using the general template: %ADD,*%. To convert dimensions from the Tango report, values in mils must be divided by 1000 to convert them to decimal inches (e.g., 050 mil → 0.050 in, 080 mil → 0.080 in).

Tango Shape	RS-274-X Code	Description & Geometry	RS-274-X Syntax	Translation Example
Ellipse (X = Y)	C	Circle	%ADD<D>C,<Diameter>*%	D10 Ellipse 010 010 → %ADD10C,0.010*%
Rd Rect	O	Obround (Rounded Rectangle)	%ADD<D>O,<X>X<Y>*%	D22 Rd Rect 080 150 → %ADD22O,0.080X0.150*%
Rect / Square	R	Rectangle / Sharp Square	%ADD<D>R,<X>X<Y>*%	D15 Rect 060 040 → %ADD15R,0.060X0.040*%
Ellipse (X ≠ Y)	E	True Ellipse	%ADD<D>E,<X>X<Y>*%	D18 Ellipse 060 040 → %ADD18E,0.060X0.040*%

5. Step-by-Step Conversion Procedure

Step 1: Analyze the Tango Report (.REP)

Open the .REP / .APT file in a text editor (e.g., Notepad or Notepad++) and locate the Aperture and Tool Descriptions section. List all D-codes along with their shapes and X/Y dimensions.

Step 2: Construct the Aperture Header Block

Prepare the list of RS-274-X definitions. Based on the sample .REP file above, construct the following header block:

%MOIN*%
%ADD10C,0.010*%
%ADD11C,0.008*%
%ADD12C,0.012*%
%ADD13C,0.018*%
%ADD14C,0.030*%
%ADD15C,0.040*%
%ADD16C,0.050*%
%ADD17C,0.045*%
%ADD18C,0.070*%
%ADD19C,0.100*%
%ADD20C,0.120*%
%ADD22O,0.080X0.150*%
%ADD23O,0.100X0.170*%

Step 3: Insert Header into Gerber Files

Open the raw Gerber layer file (e.g., CTR.GTO for silkscreen or CTR.GTL for top copper) in a text editor. Place the cursor at the very first line of the file (before existing command lines like *%FSLAX44Y44* or G70*). Paste the constructed header block. The modified file top will look as follows:

%MOIN*%
%ADD10C,0.010*%
%ADD11C,0.008*%
%ADD12C,0.012*%
%ADD22O,0.080X0.150*%
%ADD23O,0.100X0.170*%
*%FSLAX44Y44*
SFA1.0B1.0*%
G70*
G90*
G01*
D02*
D10*
X13720Y43920D02*
X13720Y43920D01*

Step 4: Verification in CAM Software

Load the newly saved file into a modern CAM viewer (Gerbv, ViewMate, or KiCad GerbView). The file should load all geometries seamlessly without throwing missing aperture/D-code errors, displaying correct line widths, pad dimensions, and shapes.