VOGONS


First post, by keenerb

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I'm attempting an ISA backplane expansion on my Tandy 1000TL.

I've gotten a ribbon cable attached to ISA bus edge connectors with pin headers; pin 1 on Tandy motherboard connects to pin 1 on a passive backplane, and so forth. The power LEDs illuminate on the passive backplane.

Nothing on the passive backplane is functional, though. It's possible I f*cked something up, but I'm also wondering if 6 - 8" is too long for the ribbon cable, problems with the ISA signal timing or something.

Reply 1 of 7, by shock__

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Generally the shorter the better - also all cables should be the same length.
Don't see 6" being overly long tho.

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 3 of 7, by whaka

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Hi,
i know it's an old topic... but, might be useful.
making travel isa signals trhu flat ribbon cable is not so easy, as it was never intended for. not like scsi and so...

one first thing to consider is impedance... every connector, every cable make an impedance change (they add resistance, capacitance and inductance). you also have to consider if transceiver are strong enough to send signals with a longer distance from receiver.
then, there's only few ground return, mostly all signals are not separated in the cable with a ground return (act as shield between two signals), so... this make crosstalk far more easier...
then... you also mix all power rail with low power signals in the same cable, it's not good too.

unless you really use very very short cables (really, very few centimeters/inch), you're gonna face all sort of issues.
i'm actually working on an isa adapter for the PS/1 2011 using flat ribbon... and well, all i can say, is the first try was a total garbage 😁

Reply 4 of 7, by Error 0x7CF

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whaka wrote on 2021-03-28, 23:10:

i'm actually working on an isa adapter for the PS/1 2011 using flat ribbon... and well, all i can say, is the first try was a total garbage 😁

Let me know how this works out. I've been researching upgrading the RAM upgrade card from 512KB to 2MB too, which I think is doable by putting on higher density chips since I think the pinout of the card slot includes the extra DRAM RAS/CAS address line. I got the old chips off with a heat gun but don't have the proficiency to put the new chips on. The memory PCB also seems to have the extra DRAM RAS/CAS line routed.

Old precedes antique.

Reply 5 of 7, by whaka

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i can confirm you can modify an actual IBM 512 KB into 2 MB, i did it.
i also comfirm all you need is any brand marked 514400 chip, then if you have the IBM 512KB extension, you can simply put a little piece of metal on pads marked R1 on the top of the extension, and you're done.
if it's another brand, like paragon or kingston, it's also doable the same way, except you have to find the resistor who put pin 23 of the edge connector at ground.

for the story, i rebuilt some ram pcb's for the 2011 and 2121 😀
the 4MB is on the road to someone for testing on the 2121, as i don't own one myself.