Josh, I would pull 58 high with a 1K to +5V on some board in your system. Should not leave it floating. Noise can trigger a signal. Yes the IEEE-696 specs allow the bus to dynamically switch 8 or 16 bits on the fly for both I/O and memory. I’m actually using it in its most extreme case right now with an 80386 (32 bits internally, jumpered to 16 bits externally) with a 24 MHz CPU clock! This system continuously switches between 8 and 16 bit access – and with our 4MG RAM board. What it will not do however is work with a board that does not recognize sXTRQ* by sending back SIXTN* for 16 bit access. Interestingly, the 80486 can actually be jumpered to do just 8 bit only access, but there are other complications with that chip which I have not yet considered/figured out. The main advantage however of the S100 bus is the ability to isolate and/or configure different computer components. The bus has the ability to have up to 16 CPUs/DMA controllers on the bus. The most I have had so far is 4 , (Z80, 6502, 80386, and 68K). John From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Crusty OMO
Sent: Wednesday, January 02, 2013 5:05 PM
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1246] S-100 board reorders John,
Thanks for clearing up the 8/16 bit issue. I checked my IMSAI, the CPU board and FP (CPA) board do not use pin 58, so this line should be floating (unless another card in the rack pulls it low). From what I know about floating input pins on TTL, they count as a 1, which is as you said "NOT low".
I can't speak for the boards in Todd's machine, perhaps he's not running the original CPU board or perhaps there has been mods to his system? The Memory protect feature was an after thought for the IMSAI, but even the IMSAI 4K SRAM card (which has the protect feature) does not use pin 58.
All I can say for sure is, there sure were a lot of custom circuits added to those old computers!
PS. I think it's really cool how the S-100 can detect 8/16 bit transfers, and if I understood it correctly, this can switch on the fly for any read/write operation. I guess it would be more correct to say BUS transfer operation?
Cheers,
Josh
From: mon...@vitasoft.org
To: n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1245] S-100 board reorders
Date: Tue, 1 Jan 2013 21:08:48 -0800 The way the IEE-696 specs were arrived at included the situation where old 8 bit (only) CPU’s/RAM/ROM/IO boards would work together. The S100Computers/N8VEM 4MG Static RAM and EPROM boards definitely work with 8 bit only CPU’s. The key S100 line is pin 58 sXTRQ*. If this line is NOT low, a IEEE-696 compatible CPU/board will assume it is talking to an 8 bit board only (separate In & OUT data lines etc) board. The issue often is the older S100 non defined lines, pins like RUN, SS, SSWDSB* UMPROT, PS, SSTACK, PINTE and the likes. Older boards often assume various uses for these pins. John Hi Todd,
The IMSAI is definitely 8 bit only. You are probably right about the 8/16 bit switching. I'm not familiar with this RAM/ROM board, but you should be able to configure it for 8 bit only mode.
I'm not an expert at S-100, but I think I read somewhere about the newer S-100 bus detecting an 8 or 16 bit card and then using the 8 DI and 8 DO lines to form a single 16 bit bi-directional data bus.
The IMSAI FP (aka CPA) and the 8080A CPU card strictly run in 8 bit mode. I'll leave it up to someone else here in this group to instruct you on how to configure your RAM/ROM card for 8 bit only.
If you do want to see my schematics for my (8 bit) RAM card, just give me your email address and we can talk.
Cheers,
Josh
> Date: Mon, 31 Dec 2012 18:35:39 -0600
> From: litte...@mchsi.com
> To: n8vem...@googlegroups.com
> Subject: Re: [N8VEM-S100:1239] S-100 board reorders
>
> I did build that board, but could never get
> it to take a deposit from the FP and from
> what I remember, there was something about
> 'every other' address step that was not displaying
> the data from memory properly.
>
> It's a complex board and I think my problem is in
> the 8/16 bit switching and the fact I truly don't
> understand it.
>
> The Eprom portion works. I burned the
> 'walking lights' program and it runs fine.
>
> I have repaired my S-100 boards and built the
> SMB with success. However, I'm not an engineer.
>
> I'll have to put it in tomorrow to refresh
> my memory.
>
> I was looking for a bare bones circuit just
> for 64K. I have one Imsai that I'd like to
> sell and it's RAM boards are flaky.
>
> Todd
>
>
>
> ----- Original Message -----
> From: "Tom Lafleur" <laf...@lafleur.us>
> To: n8vem...@googlegroups.com
> Sent: Monday, December 31, 2012 6:06:00 PM GMT -06:00 Central America
> Subject: Re: [N8VEM-S100:1238] S-100 board reorders
>
> just use the rom/ram board... cheap to build and 64k or more of fast ram
>
>
>
>
> On Mon, Dec 31, 2012 at 3:39 PM, < litte...@mchsi.com > wrote:
>
>
> I'm interested in building a simple 64K RAM board for
> the same reason. I have two Imsai's, both with
> multiple RAM card(s) with many memory chips.
>
> If someone could point me to a schematic, I'd
> like to build a few. I know Don Caprio mentioned
> earlier this year he had a project on the PBworks
> page but I don't know where to find it.
>
> I'd like to look at a few designs.
>
> Todd
>
>
>
> ----- Original Message -----
> From: "Crusty OMO" < crus...@hotmail.com >
> To: n8vem...@googlegroups.com
> Sent: Sunday, December 30, 2012 9:45:54 PM GMT -06:00 Central America
> Subject: RE: [N8VEM-S100:1236] S-100 board reorders
>
>
> Hi Andrew,
>
>
>
> Cool, thanks! Just a note on what I'm using the first (buffered) prototyping board for....
> It's currently being used as a 64K RAM card in my IMSAI. This was done to establish a working system. I'll be replacing this RAM card with the old RAM cards when I test/fix them.
> At that point, I'll repurpose this card to be an 8080 CPU, RAM & I/O card for another IMSAI system I'd like to resurrect.
>
> Cheers,
> Josh
>
>
>
>
>
>
>
>
> --
> ~~ _/) ~~~~ _/) ~~~~ _/) ~~~~ _/) ~~
>
> Tom Lafleur
> (858) 759-9692 |