#### Back to index | # Info for vic20

#### Commodore VIC20 and VC20

Cartridge Usage:
Cartridges may have any of the following extensions: .bin .rom .a0 .20 .40 .60 .prg
Files with boot-sign in it are recognized as roms. Some cartridges require more than one
image (for example, defender.60 defender.a0).
.20 files loaded at 0x2000
.40 files loaded at 0x4000
.60 files loaded at 0x6000
.a0 files loaded at 0xa000
.prg files loaded at address in its first two bytes
.bin and .rom files are loaded at 0x4000 when 0x4000 bytes long,
otherwise they are loaded at 0xa000
Note that .prg files are assigned to the quickloader (so you have to use
the -cart switch when loading rom images).

Cassette Usage:
Cassette images with the .wav or .prg extensions as well as multiple .prg files
contained within a zip file can be loaded. Zip files must be placed in the current directory,
and the contained prg files are played in sequential order.
The format for WAVs are:
8 bit (16 bit may work, but hasn't been tested), mono, 12500 Hz minimum. This has the same
problems as an original Datasette tape drive (the tone head must be adjusted to get working
(no load error...) wav-files)
Note that tape volume is DAC1 volume within the MESS UI On Screen Display Options (accessed
with the tilde (~) key in the DOS version.
Within the emulation, use LOAD or LOAD"" or LOAD"",1 for loading normal programs. Use
LOAD"",1,1 for loading programs to a special address.

Diskette Usage:
Disk drives are simulated at the moment, and only file loads from drive 8 and 9
are implemented. You can load a program file from the rom directory (*.prg,*.p00)
(This must NOT be specified on command line, start the vc20 emulation with no images specified)
You can also load a file from a d64 image (The directory command LOAD"$",8 is supported when
using d64 images).
Within the emulation, basic programs can be loaded with:
LOAD"filename",8
Machine language programs can be loaded to their address with:
LOAD"filename",8,1
When a program is loaded, type RUN or the appropriate SYS call to start it.
Note that several programs rely on more features not currently emulated (such as
loading other file types, writing...) Some games also rely on starting programs in the
floppy drive's processor (and therefore CPU level emulation of the 1541 is needed).

Quickloader Usage:
A quickloader is available via the f8 key. It supports program image files
with the .prg extension. This loads the program into memory and sets the program end
pointer. It works with most programs. The program can be started by entering "RUN" in
the emulation.

Miscellaneous Usage Notes:
Note that the pixel ratio for the PAL version is about 13/10 ! Resolution 1024x768 is good,
but only part of the screen is filled. 800x600 is acceptable. Better to define own display
mode (when the graphic driver supports this). For an acceptable display under XMESS, you can
use the following switches:
-scalewidth 3 -scaleheight 2
If you run into difficulty, be sure to start the emulation with the -log switch, and look into
the error.log file that is created in your mess directory.
See "Keys (This Machine)" in the TAB/Options menu for key assignments. Some key usages of note:
stop-restore in many cases will cause the prompt to reappear.
shift-cbm switches between upper-only and normal character set (if wrong characters are on
screen this often can help)
run (shift-stop) load and start program from tape.
The emulated light pen uses Paddle 3 x-axe and Paddle 4 y-axe.
While a normal or well written program will work regardless of the video system (PAL or
NTSC), if the screen is too wide right or low, or the screen doesn't fit in visible
area or gameplay is too fast try using the PAL (vc20) version, instead.

Known Issues:
Some PC-Keyboards do not behave well when two or more special keys are pressed at the same
time (with my keyboard printscreen clears the pressed pause key!)
The timer system only 98% accurate.
The serial bus allows simple disk support, but no printer or other devices at present.
No userport, no rs232/v.24 interface.
No special expansion modules like ieee488 interface are supported in the expansion port.
Image compatibility is quite high, see vic20.crc for a partial list. The emulation features a
rasterline based video system which should be enough for all vic20 games and programs. The
emulation supports the keyboard, as well as joysticks, paddles and lightpen, via the emulated
gameport, and simple Disk and Tape support. The expansion slot supports ram and rom
cartridges, though not special expansion modules (see known issues). For a more complete vic20
emulation, take a look at the very good vice emulator.

History and Trivia:
The Commodore VIC 20 was the successor of the CBM PET. It was designed by Bob Yannes at CBM,
he later designed the SID chip for the C64 and then went to Ensoniq to design synthesizers.
The VIC 20 used the same microprocessor and the same Basic language as the PET. It was very
popular in the early 80's. Commodore sold more than 1 million of this computer! A great range
of peripherals were developed for this computer as well as a lot of software. When it became
obsolete, Commodore replaced it by the Commodore 16 which had no success.
Note that its name came from the name of its video chip VIC (Video Interface Chip) and
its memory size : 5 KB RAM + 15 KB ROM = 20 KB ! The European VC20 stands for VolksComputer.

created on Wed May 15 07:18:19 2002