Thread: Maplin Z80 SBC
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Old 27th Apr 2020, 11:23 pm   #31
TonyDuell
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Join Date: Jun 2015
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Default Re: Maplin Z80 SBC

Quote:
Originally Posted by mikew8760 View Post
Just to fill in some of the details of my RS232 problem. In order to establish, as far as possible, the nature of the problem I used my desktop PC which has a real serial comms port. This works fine with the MICE, which sort of confirmed my suspicions about signal levels. Then I also rigged up a real Heath Robinson (younger members, Google him!) contraption with two 12V batteries and a 1488 and 1489 - that also worked fine! I have the schematic for the MICE, and it shows the 1489 Response Control pin connected via a 12K resistor to -12v, which is not the same as in the data sheet, which is at least one reason why I wished to avoid hacking this pcb.
I know you want to avoid 'hacking this PCB' but I'd try lifting one end of that 12k resistor and running the 1489 in the MICE with nothing connected to the response control pin. You might find it then works with the USB interface lead. And it's trivial to revese if it doesn't help or if you want to go back to the original circuit.
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