This article is about the reproduction of an old IEEE-488 interface card for the Commodore C64 and Commodore C128. This card was very handy if you had the Commodore SFD-1001 floppy, which had only one IEEE-488 connector. But also the old CBM floppy drives could be connected to a C64 or C128. Since such hardware has slowly become rare and hard to get, I have copied the board.
Unfortunately, I couldn't find out who the actual developer of this card is. It was distributed by the companies JANN Datentechnik from Berlin, REX Datentechnik from Hagen and WAW Elektronik from Berlin. The card from WAW Elekttronik seems to be a slightly slimmed down version, because the versions from JANN and REX contained another connector for another expansion port card, as well as an IEEE-488 socket on the board.
There are corresponding kernel versions of all 3 variants, which differ however only in the switch-on message. Otherwise the files are the same 1:1. I could find the following cards on the internet:
The card from Jann Datentechnik:
The card of Rex Datentechnik:
And the card of W.A.W. Electronics:
All 3 cards are identical in construction, only the distribution of the components and the connections differ slightly in detail. As already mentioned above, the different Kernel ROMs are absolutely identical except for the power-on message.
The card itself uses a 6821 PIA chip. The usual IEEE-488 drivers 75160 and 75161 are not used. However, if only one device is connected to the IEEE-488 bus and the cable length remains within the usual range of about 1.5m, no problems are to be expected due to the current consumption. This card has been in use for several decades and so far there are no known negative reports or defects due to this card.
Also I did not notice any problems during the tests. I also read many recommendations of this card series in forums. Personally I also liked the kernel, which has all sorts of features.
The kernel files can be found on the internet, but unfortunately I couldn't find a schematic. So I had to reconstruct the schematic from old pictures, which I had found in the internet. Since the circuit board was only executed in a double-sided layout, the reconstruction was relatively easy.
As version I chose the WAW variant, because it is the easiest to build and the easiest to trace. The first step was to make a 1:1 drawing of the old board.
Front side of the new drawing:
From this I could then derive the circuit diagram:
Afterwards I created a circuit board in KiDad. But I also used the IEEE-488 interface as board connector. So you can connect the standard Commodore IEEE-488 cable, which is always included with the Commodore IEEE-488 drives, directly and does not need an adapter or special cable.
The stock list for my card looks like this:
- C1 - C4 100nF Ceramic writing capacitors with 2.5 mm pitch
- J2 male connector 2x12 pins
- R1, R2 1k Ohm
RN1 10k Ohm resistor network star connection SIL 6-5
RN2 10k Ohm resistor network star connection SIL 7-6
SW1, SW2 = 1x 6-way DIP switch (one for SW1 & SW2 common)
- R1, R2 1k Ohm
- U1 74LS00
- U2 74LS11
- U3 6821P or 6321
- U4 EPRM 27C64 or 27C128, depending on kernel
Many parts are not needed and the costs are therefore kept within limits. The 6821P is best value for money at UTsource. You pay the equivalent of 1.80 Euro for the MC6821P. On eBay, significantly higher prices are called. But the dispatch lasts, there from Asia, accordingly longer.
And this is then the completely equipped board:
Just now I'm working on a case for this circuit board. A first draft looks like this:
But the case is not finished yet. I would provide the corresponding STL files for printing later. But I will announce this again separately.
If you want to rebuild the whole thing yourself, I have put the Gerber files in the download area.
If you have any questions or suggestions, you are welcome to use the comment field below. But I would also be pleased about criticism and suggestions for improvement.