Re: [N8VEM-S100:1653] IMSAI 8080 CPU card replacement

Ok, makes sense. I think using only 32K of RAM would be a simpler design. No jumpers to disable the on board RAM in blocks.
It is nice to be able to address other boards on the S-100 bus, perhaps someone has video cards they would like to run?

Having a full 64K means we need jumpers if we are to add some flexibility. If we keep it as-is, then you can never access memory on the S-100 bus, since all the memory is on the single board (which is fine for my application at the museum but not so cool for others who might like to access other cards).

:)J

Date: Sun, 12 May 2013 10:01:30 -0700
Subject: Re: [N8VEM-S100:1651] IMSAI 8080 CPU card replacement
From: laf...@lafleur.us
To: n8vem...@googlegroups.com

keep as much RAM as you can, 128Kx8 are just fine, its ok to not use it all....

keep it simple, do not over design it!

On Sun, May 12, 2013 at 9:54 AM, John Monahan <mon...@vitasoft.org> wrote:

Josh since there is plenty of room on the board I would keep the 64K. In fact since they are so cheap these days I would use one chip. There are no common 64X8 statics but plenty of 128x8’s static RAMS. Either waste the upper half or use banking. I have not analyzed the board thoroughly but how are you doing the ROM/Monitor. Is the PIC acting as a ROM. We could easily add a 4K ROM in place of the one of 2 RAM slots.

John

John Monahan Ph.D
e-mail: mon...@vitasoft.org

Text:    mon...@txt.att.net

From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Crusty OMO
Sent: Sunday, May 12, 2013 9:41 AM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1649] IMSAI 8080 CPU card replacement

John, I agree, the changes to bring it up to S-100 standards will be minor.

Currently, the board works stand alone. It would be nice if people could use other S-100 cards with it, eg. RAM cards to test, Video card, etc.

To keep it simple, I think we can just remove the upper 32K of RAM, CP/M runs fine in the lower 32K. The only reason I did the full 64K was because I needed to cache 4K sectors from the FLASH chip and I used 4K of the 8080A address space to do it. I would really like to go back and do this caching within the PIC address space. I just didn't have the time on my first dead line to add extra memory to the PIC. Perhaps there's another PIC chip that has 4K of RAM on the chip? I bet there is.

:)J

From: mon...@vitasoft.org
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1648] IMSAI 8080 CPU card replacement
Date: Sat, 11 May 2013 20:02:43 -0700
Josh if we can persuade Andrew to do a schematic layout. I will hammer it into IEEE-696 shape. Don’t worry Tom the additions would be fairly minor. Just want it to be able to work with our current boards

John

John Monahan Ph.D

e-mail: mon...@vitasoft.org

Text:    mon...@txt.att.net

From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Crusty OMO
Sent: Saturday, May 11, 2013 6:55 PM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1646] IMSAI 8080 CPU card replacement

Hi John,

My design definitely requires refinement to make it IEEE696 compliant. It started off as a single board replacement, but if we are going to make it into a nice board, it needs more attention to the S-100 details. I'm neck deep in my next project at the moment (building a Floppy Disk reader at the read pulse level). But when I can get my prototype back in my hands, I'll continue this design (and add the Altair connector).

I should be getting my Alair in a couple of weeks, so I'll shelve this project until then. If anyone has time to work on it, then I'd love to get more advise.

PS. How should Phantom work? Does it just override the Chip Select of the RAM?

PPS. I have the book "Interfacing to S-100 / IEE696 microcomputers" by Sol Libes and Mark Garetz. Very good book, feel free to reference any pages in it.

:)J

From: mon...@vitasoft.org
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1645] IMSAI 8080 CPU card replacement
Date: Fri, 10 May 2013 21:14:43 -0700

Absolutly minimally Josh the IEEE-696 upper address lines (A16-A20) need to be pulled to ground (via a 74LS244 or something). Take a look at the pin designations. See here:- http://s100computers.com/History.htm (bottom of page) for all the lines. Make sure Phantom like is working correctly. May want to pull to ground Data lines 7 to 15 for port I/O’s. These for starts.

John

John Monahan Ph.D

e-mail: mon...@vitasoft.org

Text:    mon...@txt.att.net

From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Crusty OMO
Sent: Friday, May 10, 2013 4:29 PM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1641] IMSAI 8080 CPU card replacement

John,

One more thing about this board...
As is, it runs great, but perhaps it could use a little more flexibility.

It has the full 64K (local on the same board), but I'm thinking perhaps it should have less or optionally allow some address space from the S-100 bus.
ie, jumper select blocks of address space that are to be gotten from the S-100 bus?

Comments?

:) Josh
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