Thread: Maplin Z80 SBC
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Old 20th May 2020, 8:44 pm   #37
mikew8760
Triode
 
Join Date: Mar 2020
Location: Bristol, UK.
Posts: 18
Default Re: Maplin Z80 SBC

Thanks Slothie for that link. I have the User Manual, but the contents of the 3 EPROMS are very useful. I've checked them against the contents of those on the board and, of course, they are all OK.
I've been checking the data path back from the 1488/89 and get to the UART, 8251. Here I find no activity on the TxD pin. I think it is correct to assume the programming of this device by the 8085 is correct - scoping the CS, WR etc I see what I presume is the data for the sign-on message being loaded into the transmit buffer. This is repeatable for processor resets, but the TxD pin remains high. So, at the moment I'm assuming that a new 8251 is needed?
I welcome any observations anyone cares to make on the above. I suppose 8251's are still available, main hassle will be extracting it from the PCB!
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