Rebuild of the IEC64W IEEE-488 card for the Commodore C64

Introduction

Unfortunately I could not 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, but they differ only in the power-on message. Otherwise the files are 1:1 the same. I could find the following cards in the internet:

The card from Jann Datentechnik:

The card from Rex Datentechnik:

And the card from W.A.W. Elektronik:

The construction of all 3 cards is identical, only the distribution of the components and the connectors 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 in the usual range of about 1.5m, no problems are to be expected due to the current consumption. This card has already some decades on the hump and so far no negative reports or defects are known due to this card.

I have also not been able to find any problems during testing. I have also been able to read many recommendations of this card series in forums. Personally, I also liked the kernel, which comes up with all kinds of features.

On the internet you can find the kernel files, but unfortunately I couldn’t find a schematic. So I had to reconstruct the schematic from old pictures I found on the internet. Since the board was only in double-sided layout, the reconstruction was relatively easy.

I chose the WAW version as it was the simplest to build and easiest to trace. So the first step was to make a 1:1 drawing of the old board.

Front side of the new drawing:

From this I could derive the schematic:

Afterwards I created a circuit board for it in KiCad. However, I additionally implemented the IEEE-488 interface as a PCB connector. So you can use the standard Commodore IEEE-488 cable, which was always included with the Commodore IEEE-488 drives, and you don’t need an adapter or a special cable. But the well known GBIP (“Centronics”) connector is also available.

The parts list for the board looks like this:

  • Capacitors
    • C1 – C4 100nF ceramic write capacitors with 2,5 pitch
  • Resistors
    • R1, R2 1k Ohm
    • RN1 10k Ohm resistor network star connection SIL 7-6
    • RN2 10k Ohm resistor network star connection SIL 6-5
  • SW1, SW2 = 1x 6-way DIP Switch (one for SW1 & SW2 together)
  • Circuits
    • U1 74LS00
    • U2 74LS11
    • U3 6821P or 6321
    • U1 EPROM 27C64 or 27C128, depending on kernel
  • Connectors
    • CN3 tub connector 2x12pin
    • GBIP socket (Centronics) 2x12pin
    • J2 header 2×12 pins


Many parts are not needed, and the costs are thus also kept within limits. The cheapest place to get the 6821P is UTsource. There you pay 1.80 Euro for the MC6821P. On eBay, the prices are much higher. But the shipping takes longer, since it is from Asia.

And this is the assembled board:

This is the cheapest way to build an IEEE-488 card for the Commodore 64 or 128. Up to now I have only tested this card successfully in a Commodore 64. But after changing the EPROM, it should work natively on the Commdore C128, too.

Download

On my GitHub account you can find everything to rebuild the map: https://github.com/DL2DW/IEC64

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