Accessing the BUSRQ and BUSACK Pins on CPU 1.0 Modules

If you have a v1.0 CPU Module and wish to use the SD Memory Dump Module, you will need access to the BUSRQ and BUSACK pins.

BUSRQ is pin 25 on the Z80

BUSACK is pin 23 on the Z80

The good news is that the BUSACK pin is not connected to anything else and is fairly easy to solder a connector to on the PCB.

BUSRQ, sadly, is not so easy.  The 5v supply from the backplane goes via pin 25 and off to 3 other pins.  You have got a couple of options from here; Modify the PCB or solder to the CPU directly.

To modify the PCB you will need to cut 3 tracks and solder 3 wires before you can connect to pin 25.  See images below;



Luckily, the tracks shown in green are on the back of the PCB, so aren’t too hard to get to with a sharp knife.  You’ll need to cut each of the connections around pin 25 and then solder links to rejoin pin 11, 17 and 24 to 5v


Good luck!

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