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Seattle Computer SCP-220A? 8088 module identification

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chris_nh

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SCP-220A ?? Curious if anyone knows what this could be for? 8088 CPU module of some type with 74LS chips and a little pin header. Hmmm... can't seem to find any info about this. (pics from ebay listing, not mine)
 
The only reference to this board I could find on the web was in a discussion forum in 1996, and what was said did not provide much information to go on.
I believe this SCP-220A daughterboard was designed to plug into the coprocessor socket on the Seattle Computer Products SCP-210 8086 processor board for the S100 bus. The Seattle Computer SCP series of S100 boards were used in systems on which 86-DOS and the earliest versions of MSDOS were developed. Since the SCP-210 ran its 8086 at 8 or 10MHz (switch selectable to 4 or 5MHz), my guess is that Seattle Computer made this SCP-220A daughterboard available for developers who wanted to be able to validate software designed for use with the IBM-PC by running the SCP-210 board with an 8088 at 4 or 5MHz.
 
Chuck(G) said:
I'm having problems trying to figure out what an 8-input NAND is for.
Click to expand...
My guess is that it is designed to look for appearance of a specific range of 8-bit addresses. One of the inputs is pulled high, one is connected directly to A10 at the 8088, five are connected to outputs of the hex inverter, and I cannot figure out what the 8th input is connected to.
I have not been able to find the SCP-210 processor board manual, which may have been able to shed further light on how this board might have worked.
 
So I just found a couple of mentions about this board at the link below. It mentions possibly a co-processor module for a Gazelle? Interesting...



Code: 
From bill at booster.bothell.washington.edu  Sat Jun  7 18:09:40 1997
From: bill at booster.bothell.washington.edu (Bill Whitson)
Date: Sun Feb 27 18:28:15 2005
Subject: Seattle Computer CPU Module
In-Reply-To: <3398F9A2.20B8@rain.org>
Message-ID: <Pine.ULT.3.91a.970607155743.29473D-100000@booster.bothell.washington.edu>

I was hoping someone wlse would know, but I'll do my best.

> In my travels, I picked up a dozen or so Seattle Computer CPU modules,
> model 220A.  Basically, it is a circuit board about 1.5" x 3" with an
> 8088, SN74LS04, SN74LS30, and a SN74LS273 chip on it.  It has an 8 pin
> header on the component side of the board, and the 40 pins of the 8088
> socket extend about .5" below the board.  Does anyone here have any idea
> what this is???  I have had them for several years and have yet to find
> out where they were used.  Thanks.

This info was obtained second hand from a guy I bought a bunch of
SCP stuff from.  Apparently a one-time friend of his work for them.
Thus - this could be wrong.  SCP made at least six models of computer
the first being Z80 machines which ran CP/M, the next few being 8086
based which ran CPM-86 or SCP-DOS (which I'm pretty sure is MS-DOS
1.0 or the immediate prdecessor purchased by MS).  The last were 8088
PC-clone type machines.  We're concerned with the 8086 machines which
apparently were equipped to take a coprocessor so as to run both
CP/M-86 and SCP-DOS/MS-DOS simultaneously.  I missed buying such a
machine by 15 minutes :(.  At any rate - I'm guessing you have a
bunch of 8088 co-processors for these machines.  The one I missed
was called a Gazelle-I so they might be for that machine.

Too bad I missed the machine - but I did pick up everything else the
guy had.  Came down to a stack of Shugart 8" drives, some CompuPro
S-100 boards and a whole bunch of SCP disks.  Now that I've brought
it up - SCP-DOS 1.0 = MS-DOS 1.0?  I'm pretty sure it is because
another disk I've got is labelled the same but says SCP/MS-DOS v1.25.

Bill

----------------------------------------------------
      Bill Whitson - Classic Computers ListOp
 
chris_nh said:
So I just found a couple of mentions about this board at the link below. It mentions possibly a co-processor module for a Gazelle? Interesting...



Code: 
From bill at booster.bothell.washington.edu  Sat Jun  7 18:09:40 1997
From: bill at booster.bothell.washington.edu (Bill Whitson)
Date: Sun Feb 27 18:28:15 2005
Subject: Seattle Computer CPU Module
In-Reply-To: <3398F9A2.20B8@rain.org>
Message-ID: <Pine.ULT.3.91a.970607155743.29473D-100000@booster.bothell.washington.edu>

I was hoping someone wlse would know, but I'll do my best.

> In my travels, I picked up a dozen or so Seattle Computer CPU modules,
> model 220A.  Basically, it is a circuit board about 1.5" x 3" with an
> 8088, SN74LS04, SN74LS30, and a SN74LS273 chip on it.  It has an 8 pin
> header on the component side of the board, and the 40 pins of the 8088
> socket extend about .5" below the board.  Does anyone here have any idea
> what this is???  I have had them for several years and have yet to find
> out where they were used.  Thanks.

This info was obtained second hand from a guy I bought a bunch of
SCP stuff from.  Apparently a one-time friend of his work for them.
Thus - this could be wrong.  SCP made at least six models of computer
the first being Z80 machines which ran CP/M, the next few being 8086
based which ran CPM-86 or SCP-DOS (which I'm pretty sure is MS-DOS
1.0 or the immediate prdecessor purchased by MS).  The last were 8088
PC-clone type machines.  We're concerned with the 8086 machines which
apparently were equipped to take a coprocessor so as to run both
CP/M-86 and SCP-DOS/MS-DOS simultaneously.  I missed buying such a
machine by 15 minutes :(.  At any rate - I'm guessing you have a
bunch of 8088 co-processors for these machines.  The one I missed
was called a Gazelle-I so they might be for that machine.

Too bad I missed the machine - but I did pick up everything else the
guy had.  Came down to a stack of Shugart 8" drives, some CompuPro
S-100 boards and a whole bunch of SCP disks.  Now that I've brought
it up - SCP-DOS 1.0 = MS-DOS 1.0?  I'm pretty sure it is because
another disk I've got is labelled the same but says SCP/MS-DOS v1.25.

Bill

----------------------------------------------------
      Bill Whitson - Classic Computers ListOp
Click to expand...

That is also the link I found, which I referred to above.

I think this recollection posted by "Bill" might have been a bit fuzzy. SCP manufactured two 8086 CPU board models (the SCP-200 and the SCP-210) that were used in their "Gazelle" computer systems based on the S100 bus. Only the SCP-210 had a coprocessor socket. Bill's note talks about needing a coprocessor to run CP/M-86 and MSDOS simultaneously, but that does not make sense since (a) both operating systems could have been run using the same 8086 processor board and (b) these two systems would not truly run "simultaneously" on an S100 system with use of a simple daughterboard. That is why I speculated there was perhaps an alternative reason why one might want to "downgrade" an 8086 CPU board with use of this 8088 daughterboard. Unfortunately, since documentation for the SCP-210 and SCP-220 boards does not seem to be available, we cannot be certain.
 
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If it's a downgrade module (8088 module to run in 8086 socket?), I first wonder if it would it work in any 8086 socket, or if the header pins need to be connected to something(s) for operation. If so, I was looking at pictures to see if I could discern an obvious place to connect on the SCP-200 or SCP-210, and there's nothing definitive to tell from the pictures, but I suppose it could connect somewhere on the SCP-210. Strange downgrade perhaps and probably not a big seller?? :LOL: The CPU is 5mhz, which doesn't fit the speed of the cpu boards, except for the SCP-200 at 4mhz? I understand the SCP-200 also ran at 8mhz, and the SCP-210 is either 8 or 10mhz.

Also interesting to note, the 8087 add on board is SCP-910A rather than something like scp-20x or 21x... SCP part numbers are interesting and I have yet to find a list.
 
My guess is that it's just a board to provide an I/O port to an 8088. Could not even be for any SCP system, but rather a plug-in for a 5150 or the like. The IC dates put it at earliest 1985. Perhaps a debugging aid.
 
chris_nh said:
If it's a downgrade module (8088 module to run in 8086 socket?), I first wonder if it would it work in any 8086 socket, or if the header pins need to be connected to something(s) for operation. If so, I was looking at pictures to see if I could discern an obvious place to connect on the SCP-200 or SCP-210, and there's nothing definitive to tell from the pictures, but I suppose it could connect somewhere on the SCP-210. Strange downgrade perhaps and probably not a big seller?? :LOL: The CPU is 5mhz, which doesn't fit the speed of the cpu boards, except for the SCP-200 at 4mhz? I understand the SCP-200 also ran at 8mhz, and the SCP-210 is either 8 or 10mhz.

Also interesting to note, the 8087 add on board is SCP-910A rather than something like scp-20x or 21x... SCP part numbers are interesting and I have yet to find a list.
Click to expand...
The SCP-210 had a coprocessor socket - intended for an 8087, but we don't know if they made other changes to accommodate a daughterboard.
The SCP-210 ran its 8086 at either 8 or 10MHz (depending on the speed of the 8086 installed), but there was a switch to halve the clock frequency to 4 or 5MHz.

Indeed, I have also been unsuccessful at finding a complete SCP product listing.
 
I made a schematic of the SCP-220a ... not sure if this is 100% accurate, but I think it's correct. The LS273 inputs are D0-D7 and the outputs all go to the pin header. Address lines A8-A11 are used as selection criteria along with S0-S2, but I'm having a hard time figuring out what it is selecting for. The pullups on S0-S2 don't really make sense in my mind and I'm confused about the NAND gate output to the clock pin on the LS273... seems like it is backwards and would basically output everything all the time on the pins. I've assumed the 8088 is configured in max mode, but maybe it's for min mode... not quite sure. Can anyone decipher what this is doing?
 

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I came back to it this morning for a look with fresh brain cells, and I'm pretty sure it's an IO port for output. The S0-S2 status works for S0=0, S1=1, S2=0 which is IO write in maximum mode. So the address of A11=0, A10=1, A9=0, A8=0 along with IO Write signal will transfer the data to the Q outputs of the ls273. ls273 transfers the data to Q upon the rising edge of CP, which will happen when the NAND inputs first all go high (NAND output becomes low), then the S0-2 status lines change between T3 and T4 during the bus cycle and the data is then latched to the outputs Q.

I think this makes sense and it's basically just an IO port built onto the CPU module. Now I wonder if this thing will work in a 5150 ?? Hmm... I guess I'll have to try it to find out!

I'm still wondering what SCP intended this to be. Hmm again
 
I thought that all SCP systems used the 8086, however I haven't researched the subject. But again, what, other than debug, is an output-only port good for? No handshaking, so that kind of limits it.
 
Sorry to resurrect an old thread, but this card will in fact boot up in a 5150. See attached photos (sorry they are so big). I do not know if there are any diagnostic programs or BASIC commands that could reveal anything else about the module. My bet is that this was simply produced by SCP to sell DOS under Seattle Computer's perpetual license since
1. It doesn't appear to have any real purpose (or at least the purpose is unknown, so maybe it had some very obscure purpose)
2. It was built in mid-1986 shortly before SCP sued Microsoft. After Microsoft settled with SCP and reclaimed SCP's DOS license, these would have been worthless.

Shown booting in a Rev A machine in the photos below.


IMG_1295.jpgIMG_1296.jpg
 
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