ISA Bus in the 1000 series

[Great Hierophant]

I hear from various sources that the ISA bus as implemented in the Tandy 1000 series, 8/16bit, lacks the -5v connection. Is this true? Does this affect all models? I have a rare 8-bit ISA sound card, which requires 50mA on the
-5v rail that I would want use in one if I buy one, so I must make sure.

[kb2syd]

From the T1K technical reference:
BO5 - 5VDC
IBM PC -5VDC is always available.
TANDY 1000 -5VDC is not installed on the I/O bus, but a modification is
available through an authorized repair center.


So, find the trace, and add -5v to it. There are a few other signals not there. See page 10 of the techref (page 16 of the file) from tvdogs model 1000 site.

ftp://ftp.oldskool.org/pub/tvdog/tandy1000/documents/1ktech.zip

[daflory]

As far as I can tell from the Tandy 1000 SX tech guides, the 8-bit bus provides +5, +12, and -12. There's no mention of -5V, so I think your sources are probably right.

[kb2syd]

I got my information directly from the Technical Reference for the 1000. Page 10 is a cross reference of the Tandy implementation of the ISA bus and IBMs ISA bus. Most of the other differences outlined on this page are either due to there being no DMA on the 1000 motherboard, or just naming convention discrepancies.

Of course we all know that Tandy's technical references are all 100% correct :-)

[daflory]

I got my information directly from the Technical Reference for the 1000. Page 10 is a cross reference of the Tandy implementation of the ISA bus and IBMs ISA bus. Most of the other differences outlined on this page are either due to there being no DMA on the 1000 motherboard, or just naming convention discrepancies.

Of course we all know that Tandy's technical references are all 100% correct :-)

Yeah, they are pretty dodgy, I agree. :) (BTW--I think our responses were simultaneous...I posted before I saw yours)

I was using the 1000SX tech manual, and the SX does have DMA on the mb (as does the TX). One of the reserved lines also goes directly to the sound out...but I'm not sure if anything ever used it.

There was a Disney/Tandy sound board that I think I remember being made for 1000's that might have.

I didn't know about that hack, thanks. (I also didn't know that ANY ISA cards used -5v!) In general, any 8 bit card that will fit will work in the SX or later, as long as you disable the on-board IRQ if necessary.

GH, what sound card are you using?

[Great Hierophant]

GH, what sound card are you using?

I am using, in my opinion, the best sound (and probably most expensive) card ever made for the ISA bus: the Roland LAPC-I. All my other sound cards, even my IBM Music Feature Card, do not use a -5v line.

[chuckcmagee]

OMG - the ROLAND!!! (..bowing..) Sniff, sniff, I never could afford one of those, had to make do with a Thunderboard and a PAS-16.

[Great Hierophant]

The Roland card really works best on IRQ2, which coincidentally, is also the IRQ that a Tandy hard drive is supposed to use. Fortunately, IRQ5 is usually free and its the card that controls which IRQ will be used, not the BIOS.