C128 BASIC extension for VDC graphics
Copyright (c) 2026 Graham (Francesco Gramignani)
Version 2.04
Revision 9/5/2026
https://graham-it.itch.io
https://github.com/graham-it
https://csdb.dk/scener/?id=40810
Wedge80 is a program that extends the Commodore 128's BASIC 7.0 to take advantage of the graphics capabilities offered by the MOS 8563 VDC (Video Display Controller) chip, which is normally used only in 80-column text mode.
Wedge80 is compatible with the PAL versions of the C128/C128D, equipped with 16k or 64k bytes of video RAM dedicated to the VDC chip, and with the official BASIC 7.0 ROM revisions released by Commodore (1985/1986).
To access the VDC chip's graphics capabilities, Wedge80 uses the same instruction set as BASIC 7.0, extending the number and range of supported parameters. Thus, Wedge80 can handle both VDC and VIC-II graphics, ensuring full compatibility with existing software.
| Commands | Description |
|---|---|
| GRAPHIC | Selects the current screen mode |
| COLOR | Sets a color for the selected source |
| SCNCLR | Clears the selected screen mode |
| LOCATE | Places the pixel cursor to a specified position |
| DRAW | Draws dots, lines, and shapes |
| BOX | Draws a BOX on the screen |
| CIRCLE | Draws circles, ellipses or arcs |
| PAINT | Fills an area starting from a specified position |
| SSHAPE | Saves an area of the the screen into a BASIC string variable |
| GSHAPE | Draws a shape stored in a BASIC string variable |
| CHAR | Displays a string of characters on current bitmap/text screen |
| AUTOFAST | Enables the AUTOFAST mode (FAST/SLOW to disable) |
| HELP | Displays system status or Online Gude |
| QUIT | Returns to BASIC 7.0 |
| Functions | Description |
|---|---|
| RGR | Returns the value of the current screen mode |
| RCLR | Returns the value of the color source specified |
| RDOT | Returns the current bitmap coordinates or pixel status |
| RWINDOW | Returns dimension information about the current screen or window |
| POS | Returns the cursor position within the current text screen window |
Wedge80 is available in two versions:
- WEDGE80 full version
- WEDGE80LT light version (without the 'Online Guide')
To install Wedge80, after inserting the disk containing the program, simply load and run one of the two versions with the following commands:
- DLOAD "file name" (equivalent to LOAD "file name",8)
- RUN
or:
- RUN "file name" (loads and runs)
During installation, the amount of memory available on the VDC chip (16k or 64k bytes) is automatically detected to adapt the program to the machine in use.
Wedge80 offers 144 theoretical combinations for configuring bitmap graphics using the VDC chip, allowing you to separately select the horizontal and vertical resolutions (up to 840 x 256 pixels) and the size of the color cells (down to 8x2 pixels).
VDC graphics can be activated using the command:
- GRAPHIC mode[,clear][,h/res][,v/res][,color]
| mode | Graphics mode | clear | Clear flag |
|---|---|---|---|
| 0 | VIC-II 40-column text | 0 | Do not clear (defalut) |
| 1 | VIC-II bitmap (320x200) | 1 | Clear screen (and reset coords) |
| 2 | VIC-II split screen bitmap | ||
| 3 | VIC-II multicolor bitmap (160x200) | ||
| 4 | VIC-II split screen multicolor bitmap | ||
| 5 | VDC 80-column text | ||
| 6 | VDC bitmap |
| h/res | Horizontal mode | v/res | Vertical mode | color | Color mode (cell size) |
|---|---|---|---|---|---|
| 0 | 320 pixels | 0 | 128 pixels | 0 | Monochrome |
| 1 | 360 pixels | 1 | 144 pixels | 1 | 8x8 pixels |
| 2 | 640 pixels | 2 | 176 pixels | 2 | 8x4 pixels |
| 3 | 720 pixels | 3 | 200 pixels | 3 | 8x2 pixels |
| 4 | 800 pixels | 4 | 240 pixels | ||
| 5 | 840 pixels | 5 | 256 pixels |
Once the VDC bitmap mode is activated, you can use the following command to draw a point or line on the screen:
- DRAW [mode][,x0,y0][<TO|,> xn,yn][...]
| mode | Drawing method |
|---|---|
| 0 | Clear pixels |
| 1 | Draw pixels (default) |
| 2 | XOR with the pixels already on the screen |
More details on Wedge80 extended commands and functions are available in the docs files included.
The full version of Wedge80 comes with an 'Online Guide', which is installed in the upper part of the RAM block 1, normally used for storing BASIC variables.
To view the complete list of Wedge80 commands and extended functions, simply enter the following command at the BASIC prompt:
- HELP +
Additionally, you can get detailed information about a specific command or function using the following syntax:
- HELP keyword
Where 'keyword' is the word used to identify the command or function you're requesting information about.
When Wedge80 is started, AUTOFAST mode is enabled by default. This allows extended Wedge80 commands to be executed in FAST mode (2 MHz), then automatically reverts to SLOW mode (1 MHz) upon completion.
- AUTOFAST (enables AUTOFAST mode)
- FAST/SLOW (restore standard modes)
Using keyboard in direct mode, the 'ESC X' sequence allows you to quickly switch between 40-column and 80-column text mode. When the 'ESC X' sequence is detected and the VDC is in bitmap mode, the 80-column text mode is automatically restored, transparently to the user.
Once installed, Wedge80 offers a function library that allows you to use some of its graphics routines directly from a machine language program (like the Sketch80 demo).
This is done via a Jump Table, which ensures compatibility with any programs developed with this library, even if an updated version of Wedge80 is released.
| File name | Description |
|---|---|
| EASY GRAPH | Plots a user-defined mathematical function |
| GRAPHIC SAMPLE | Draws some geometric shapes |
| MARBLE | Demonstrates the use of the CIRCLE command |
| MONOSCOPE | Tests the various graphics modes of the VDC |
| QIX | Runs a simple animation in color or monochrome mode |
| RACING CARS | Demonstrates the use of the SSHAPE/GSHAPE commands |
| SCREEN SAVER | Shows 3 types of user-configurable screen savers |
| SKETCH80 | An example written in ASM that uses the Wedge80 Library |
| SPACESHIP | A scene made by combining multiple modules |
Wedge80 v2.04 (c) 2026 Graham