Parallel IEEE 488 interface for VC1541

(c) 64er magazin

Someone asked me about the parallel IEEE 488 interface for the VC1541, that has been published in an early issue of the famous german "64er" magazin. Well, I don't know if this magazin still exists (long out of the scene) but then I have this old issues in case I need to repair my interface.

I have redrawn the schematics now, so there is a nice schematic instead of my sketchy hand-drawn one. People who know what they are doing can see how to produce such a board.

Disclaimer

There is absolutely NO WARRANTY, neither expressed nor implied! Noone can be held responsible for any damage arising from the use or building of this interface or even from reading these pages! I do not claim nor guarantee that the hardware and software can be used for anything useful!

The nicely drawn schematics are available in vc1541-ieee.png and vc1541-ieee.ps. The socket on the right is the IEEE488 connector. In vc1541-ieee.desc.txt you find the schematics in a text file together with some info how to build it. Hint: The ouput lines PA0-7, PB0-7 (Pins 2-17) and CA1 and CA2 (Pins 40,39) are not connected through to the motherboard! Note that the IC and socket labeled "UC3" has to be the VIA 6522 that is connected to the IEC bus. This might be different on different versions, it is UC3 on my 1540048-01 circuit board(short board). The interface is basically modelled after the 2031 schematics, the IEEE488 sister drive to the VC1541.

To use the interface the VC1541 needs a new ROM. In the 64er magazin they listed a program vc1541-ieee.mkrom.prg to read and patch the original VC1541 ROM. You can read an ASCII listing in vc1541-ieee.mkrom.txt. Because I was too lazy to type in the whole program, only the very necessary parts are there. So before you start, you have to do a "POKE 56,80" to protect the area above $5000, where the modified ROM is saved. When the program has finished, you have to save the area from $5000 to $6fff with a machine language monitor. This file has to be burned into an EPROM that replaces the ROM with the upper half of the VC1541 DOS. For the exact location please see http://www.funet.fi/pub/cbm/schematics/drives/new/1541/index.html. The original 2031 ROM is different from the VC1541 ROM in both ROM chips, but the patch manages to get the changes into one ROM chip only, so only one EPROM is needed.