UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Nascom repair

SiriusHardware · 25th Oct 2017, 10:27 pm

Anyone know if the MK3881 is basically just some other manufacturer's clone of the Z80-PIO, or a distinct device in its own right?

The control and data registers for port A appear to be mapped to I/O addresses 0x07 and 0X05. (Port B Control / Data registers are at I/O addresses 0x06 and 0x04).

As both I/O ports look to be undedicated / available for user use, possibly the simplest observable thing to do would be to output a running binary count to either Port A or Port B and hope to observe activity on all of the port pins. If that works, then you really can be sure that the processor subsystem is essentially working.

Edit: A quick shufty around the 'net does seem to suggest that the MK3881 is a Mostek clone of the Z80-PIO.

25th Oct 2017, 10:27 pm	#14
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,575	Re: Nascom repair - Looking for clues please Anyone know if the MK3881 is basically just some other manufacturer's clone of the Z80-PIO, or a distinct device in its own right? The control and data registers for port A appear to be mapped to I/O addresses 0x07 and 0X05. (Port B Control / Data registers are at I/O addresses 0x06 and 0x04). As both I/O ports look to be undedicated / available for user use, possibly the simplest observable thing to do would be to output a running binary count to either Port A or Port B and hope to observe activity on all of the port pins. If that works, then you really can be sure that the processor subsystem is essentially working. Edit: A quick shufty around the 'net does seem to suggest that the MK3881 is a Mostek clone of the Z80-PIO. Last edited by SiriusHardware; 25th Oct 2017 at 10:33 pm.