Re: 1861 Replacement

Peter Renaud


Thanks for the heads up.
I have the SR in U4 as I had to revise that circuit because of my Nx lines being active low.
I have attached my current draft design schematic and PCB for your review.
I am in the process of revising it before sending to the JLCPCB fab.
The expansion board is a prototype that connects to my SBC 1802 V3 card.
It provides the CDP1861 Rev B circuit, a PS/2 interface (make characters only) and a I/O port which replaces the one on the V3.


From: <> on behalf of the-eagle@... <The-Eagle@...>
Sent: Monday, September 14, 2020 12:58 PM
To: <>
Subject: Re: [cosmacelf] 1861 Replacement
Peter, It just came to mind that in my Rev. B and Rev. D replacement circuit I have a minor problem that I have since corrected in my Rev. E which was made 2 weeks (July 20, 2019) after I made the Rev. D. The error in the forming of the SR (Set/Reset) flip-flop U4 and U5 to make, these are non-matching gates, the results are that the DIS ON will turn the circuit in however the DIS OFF will NOT turn the circuit off. I have now made the DIS ON, DIS OFF, SR flip-flop out of 2 gates in U4. Please see the attached Rev. E schematic to see the change I made on the DIS ON and DIS OFF lines.



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