Feedback on Idea, Using ISA cards for Breadboarding I/O

Thread Starter

HalfMadDad

Joined Jun 10, 2016
30
Hi

This is sort of a continuation of this thread:
http://forum.allaboutcircuits.com/threads/interfacing-pc-to-circuit-without-firmware-involved.124885/

There are new motherboards that have ISA slots still and then there are really old computers.

My understanding is that ISA cards often used to have no firmware and were controlled by the PC's CPU.

I am attracted to desktop computing more then "embedded".

I have many things I want to do but basically right now I am thinking of getting a ISA prototype board:
http://www.futurlec.com/Protoboards.shtml

am using it to bread board circuits. I was thinking I could use a 16 bit ISA bus to control 14 devices by SPI

Does anyone see any downsides to this approach, am I about to go over a cliff :) ?
Thanks-Patrick
 

MrChips

Joined Oct 2, 2009
19,280
There is nothing wrong with doing basic input/output on an ISA prototype board but you have two challenges ahead of you if you have never done this sort of thing before:

1) Hardware
2) Software

1) Hardware. You will need interfacing glue to interface with the ISA bus. This consists of an 8255 Programmable Peripheral Interface (PPI), bus drivers and address decoders. Don't get that ISA prototype board from Futurlec. Find one that has the interface circuitry already laid out on the board. If the board comes without ICs you can add your own.

2) You have to find a software development platform which will allow you to do what you want. Visual Basic is a good candidate.
 

MrAl

Joined Jun 17, 2014
6,513
Hi,

Back when this kind of buss was common, i built an i/o card that was to be used for controlling a digital oscilloscope. I used discrete logic ic's. That was also when you could write an ASM program to interface with the cards right from DOS.
The CPU lines would go right to the card and the address lines decoded into an i/o port address. I think i used something like a 74xx138 for the decoding, and that gave me 8 ports right off the bat. Still have the card somewhere but it does not fit in any of my computers now :)

If i were you though today i would use the PCI buss at the very least so it works in many modern computers.
 

Thread Starter

HalfMadDad

Joined Jun 10, 2016
30
Hi MrAl

Thanks for your post! Yes I am thinking about PCIe actually. I thought that the ISA bus was pretty much just GPIO lines but there appears to be some signalling as well. I am looking into a PCIe to local bridge and I am trying to study passsive boards

Thanks again
 

JohnInTX

Joined Jun 26, 2012
3,810
FWIW, here is the schematic of an ISA interface board I did way back when. While I agree with the others that a more modern bus might be better, this at least shows how it was done on the original PC/XT/AT stuff. The ROMs on page 3 are for BIOS extensions and application code that MS-DOS would install on power up to provide hooks for programs to access the board. The original application was for computer vending kiosks or something like that - that's what the opto interfaces were for. We used to use them with a big proto area on some of the boards so that we could adapt various hardware to the PC environment.

I probably still have the PAL (PAL!) logic descriptions and maybe the PC gerbers as well if you are interested.

Man, I'm old....
 

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HalfMadDad

Joined Jun 10, 2016
30
Hi John

Thanks very much for this. I have saved the schematic and I am going to study this along side a 8255 datasheet.

I don't want to take more of your time but if you come across the Gerber file that would be great.

Thanks again-Patrick
 

JohnInTX

Joined Jun 26, 2012
3,810
Looks like the PCB source files are long lost casualties. Based on the dates, I'd guess the PCB was pen-on-mylar plots instead of Gerbers with archives on floppys... Sorry.
But I've attached the logic source for the two PALs which will show how the 8255 and on board memories were decoded.

Have fun.
 

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