(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.
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.