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ISA bus thoughts

PhilipA

PhilipA

Experienced Member
Joined
Aug 4, 2013
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476
Location
Larose, LA, USA
Okay, as y'all probably know, I have a Compaq luggable. I've been adding to it and changing it up in non-destructive ways. I like to be able to pull it all out and stick the original bits back in if possible.

However, the machine is limited in size by the chassis, and as such it only has (only!) five ISA slots. The first two are populated by the two cards you get with the base system, the floppy/parrallel card and the CGA video adapter.

The remaining three slots in my system have the Ethernet card, the CF hard-drive card and a Diamond Flower MF-100 card (hosts RTC, serial, parallel, game and 384kb of RAM).

I'm aware that the timing on the ISA bus is pretty critical, being as it's a direct connection to the CPU but I was looking and there are a couple modern cards that are very thin compared to expansion cards of yore, and they don't need the same cooling.

Would it be possible to branch a single ISA slot into two? From what I read it's a genuine bus topology with the address capability for up to 6 slots. There's physically enough space for two thin cards in a single ISA bus bay, so long as they do not need access via the rear of the case. There's also space vertically in this chassis.

Possible? Electrically improbable or unreliable? Technically impossible due to the way a single slot works? Enlighten me :)

--Phil
 
I don't see why not. The original 5150 had only five slots. It might be easier to find a floppy+everything card (parallel port, serial port, clock) multifunction card and save yourself some trouble.
 
Possible? Yes. That is after all what the expansion boxes IBM did. And I think there was a slot adapter/splitter from a third party. Lots of work to implement if you don't already have one.

The other drawbacks are the limits of power draw per slot and over the collective slots of the portable and the need to keep the cards fixed in place. Loosely held cards may not be ideal in a portable system.
 
The slot was successfully powering a Plus HardCard. The joint power consumption of the two modern cards I'd like to have will be less in aggregate.

It'll also be fixed in place using the mounting screw holes at the back, just fitted with a blank in the slot hole itself. Making a small frame would not be hard.

I was thinking of trying to find a card that did more than the MF-100, specifically the same functions but with the addition of a floppy controller. Unfortunately most of those seem to be for 286-class machines only, integrating an ide controller etc.

I was looking at that image, would be good but the cards need to be vertical to work with the rest of the cards/space.

Phil
 
PhilipA said:
The slot was successfully powering a Plus HardCard. The joint power consumption of the two modern cards I'd like to have will be less in aggregate.

It'll also be fixed in place using the mounting screw holes at the back, just fitted with a blank in the slot hole itself. Making a small frame would not be hard.

I was thinking of trying to find a card that did more than the MF-100, specifically the same functions but with the addition of a floppy controller. Unfortunately most of those seem to be for 286-class machines only, integrating an ide controller etc.

I was looking at that image, would be good but the cards need to be vertical to work with the rest of the cards/space.

Phil
Click to expand...
You could piggy back one of those adapters on top if you enough head room.

Also the 8 bit portion 16 bit multi i/o cards will work fine and give you fdd, parallel, possibly two serial and possibly a game port. The IDE section will just hang over the back it there's room. Trim it off even. The good thing is there's still plenty of them around. Added bonus is you can access 1.44meg floppies using a tsr if need be.
 
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Caluser2000 said:
Should be able fit an ISA adapter similar to those fitted in slimline chassis that use regular generic at class mobos. http://3.bp.blogspot.com/_Svwa4PMZAQc/TTBb0KF-V6I/AAAAAAAAAU8/I0MM4TD-mz4/s1600/isa+slots.png Might even be able to trim the back portion off.
Click to expand...
I've got a couple of them:

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One has five slots and the other has six. There's no reason you couldn't just use the 8-bit slot and ignore the 16-bit part. It would be like putting an 8-bit card in a 16-bit slot on the motherboard.
 

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If you'd like the green/copper PCB shown above (the one with two 8-bit and three 16-bit slots) PM me with a reasonable offer and I'll test all five 8-bit slots on it for you. I will be testing the riser's slots with a CGA card. Or, if you have another preference I could perform the tests with another card, e.g., MDA, memory expansion or even floppy controller.

Also, where are you located? If you add it to your profile no one will ever ask you again as it will appear in every post. :)
 
So, with the two options: 1) Hardware addition to provide one extra ISA slot. 2) Find a multifunction card that has a floppy controller on.

1) is a possible hack, I'd probably have to do it with Veroboard first as a proof of concept.

2) Are there any 8-bit cards out there that offer all in one:

a) RAM expansion (384kb)
b) Floppy controller (720kb is fine)
c) RealTime Clock
d) Serial port(s)
e) Parallel port

That would be the minimum requirement, anything extra is a bonus. I leafed through STASON and didn't find anything that fit the bill. Most of them have the same functional capability as the MF-100 in there right now, less the floppy drive controller.

--Phil
 
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