Very nice work on re-entering the schematic. However, there were some changes that the group discussed and I would like a chance to implement, test and build a prototype first.
This board shouldn't have a DB connector on it, just the header. The DB connector(s) should be mounted on the chassis of the machine.
The Alair front panel connector, if I'm not mistaken, is a pin header, with 0.156" spacing 0.045" square post. I think it looks something like Digikey's part number A1974-nd. I've got a bunch of these connectors and will try it out with my Altair when I can.
Subject: RE: [N8VEM-S100:1773] IMSAI 8080 CPU card replacement
Date: Thu, 8 Aug 2013 17:32:00 -0400
Hi! Here are the changes to the S-100 8080 CPU board. Please review and send me any changes and/or corrections.
I added a standard PC serial dual row header for the serial port. I really don’t think any sort of DB25 or DE9 is going to fit within the S-100/IEEE-696 form factor without bumping up against the chassis or causing other problems. There is no room for it on the top of the board. We can rework the PCB layout though if that would help. I don’t think it will be a problem to use a short ribbon cable to the DE9 connector since it is common place on S-100 boards.
Also I still need some schematic inputs and part dimensions etc for the Altair front panel connector. I presume it would go directly under the IMSAI front panel connector? Please someone send me the changes and I will patch it in the schematic.
Thanks and have a nice day!
Andrew here is my first pass at trying to hammer the 8080 “Front panel” board into IEEE-696 shape.
I’m not entirely comfortable with it as I don’t understand some aspects.
Josh why for example is the Data out line (S100 pin 39) the only one coming off the board to the S100 bus.
As the board looks it will never access any other off board RAM/ROM.
It’s unclear to me also how I/O ports are addressed. Looks like ALL ports go into PIC. Is there a range we could select for so that are outside that range and go to the S100 bus/other cards.
I think the only way we will get INT’s to work would be to play with a prototype.
Attached are my initial “suggestions”
Hi John! Thanks! Here are the most latest S-100 8080 CPU board schematic and PCB layout. Please review and send me any changes and/or corrections.
Ignore the J1 (DB25M) since I don’t know where to put it and it doesn’t make a lot of sense where it is. Maybe this should be a 13x2 dual row header? DB25M has nowhere to go with the present layout and wouldn’t most builders just use a ribbon cable? Also ignore the extra filter capacitors since those are just spares for any additional chips that will probably get added later.
I have not started trace routing since it may be a couple iterations yet before we’re ready to set an initial PCB layout.
Any input from anyone is greatly appreciated. Also what is the Altair FP connector look like? How is it connected?
Guys, I’m wondering if it would make sense to modify that board more. I see there is a decent demand for it. If people are not in a hurry it might make sense to modify it could act as a bus master like the old style IMSAI/Altair accepting DMA etc. This would require adding a true data bus in and out lines, 2MH clock etc. so it could actually be used with other S100 cards in the bus.
I (or others), could take a stab at this, but it probably would be best to do a prototype board first.
We need to have both Altair and Imsai front panel connector.... Same signals, different connector
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