I wish to create a new DMA/RAM expansion card for the Tandy 1000 line.

[Eudimorphodon]

The SX was the first 1000 family machine to have the DMA controller integrated onto the motherboard. I'm guessing Tandy concluded that since they didn't need any "extra" lines to implement the DMA control bus anymore they might as well eliminate their proprietary mapping of those pins.

Thanks to some help in the other thread I was able to solve the particular issue that was vexing me, IE, not actually being able to use IRQ2 for the Realtek 8019AS ethernet card despite the hardware supporting the mapping. As discussed on that thread IRQ2 is itself kind of an interesting edge case for usability; it's fine with XT-vintage hardware and software, but because the AT architecture pirates IRQ2 and attaches the same pin to IRQ9 on the second interrupt controller apparently some software that otherwise runs on an XT, like the "native" packet driver for the Realtek card, won't run with the card on IRQ2 because it makes AT-centric assumptions. Technically it's a stupid bug in the driver that could probably be easily fixed, but I wonder if there are other examples of that sort of thing lurking out there just waiting to bite.

(The workaround here was leveraging the card's NE2000 compatibility and using an 8-bit compatible NE2000 driver that allows manually specifying the I/O and IRQ settings accurately.)

Another thing I've started noticing is there really does seem to be a non-trivial amount of DOS software from the early 90's and later that doesn't like 8088 CPUs but will run on V-20s. So far I've left the 8088 CPU in my HX test rig, and I can confirm that in addition to the current version of Cutemouse being a problem there seems to be an issue with DOS Kermit; a weird, funky issue that's going to force me to break out my second eBay V-20 to absolutely confirm it. Fun stuff!

 

[blackepyon]

The great thing about the Tandy 1000 line, unlike the early IBM 515X series, is that pretty much everything you needed to function was already on board, and didn't cost you an arm and a leg.

I contemplated, briefly, whether or not it would be possible to gang another 8259 to add more IRQs to the EX/HX. I think it IS possible, but it would require either cutting traces, or socketing a special daughterboard, making a custom psudo "16"-bit expansion bus for the extra IRQs, etc.... Not really worth it, IMO, but could be fun as a thought experiment.

 

[dJOS]

Well, I've been having some fun with in-depth testing. So far I think my hardware is actually just fine, but it's kind of amazing some of the machine-specific quirks I've run into.

Does anyone who's keeping an eye on this thread happen to use an Ethernet card in their EX/HX using whatever kind of adapter you've made, bought, or otherwise magic-ed into existence? I'd be curious to hear what you're using and what hardware resources you've assigned it.

I'm using a WiModem 232 for all external comms - works great for my needs.

 

[blackepyon]

The SX was the first 1000 family machine to have the DMA controller integrated onto the motherboard. I'm guessing Tandy concluded that since they didn't need any "extra" lines to implement the DMA control bus anymore they might as well eliminate their proprietary mapping of those pins.

They still had pin B8 (slot-8/card select) as an "audio in." I'm guessing that was for the modem card?

 

[Eudimorphodon]

The great thing about the Tandy 1000 line, unlike the early IBM 515X series, is that pretty much everything you needed to function was already on board, and didn't cost you an arm and a leg.

Oh, don't get me wrong here, I'm in no way ragging on the Tandy 1000. The... eccentricities, I'm running into are all part of the fun. I'm just getting amused at how the well of differences between these machines and regular old boring PCs doesn't seem to be showing any sign of bottoming out.

 

[Eudimorphodon]

They still had pin B8 (slot-8/card select) as an "audio in." I'm guessing that was for the modem card?

Have you checked the schematic yet to see where that goes? Does it just go to the audio amplifier circuitry (via a crude mixer?) to act as a remote speaker for a card, or is it more sophisticated than that.

Ironically the EX modem has a big 'ol speaker on it, so I'm kind of doubting it used it.

 

[blackepyon]

Have you checked the schematic yet to see where that goes? Does it just go to the audio amplifier circuitry (via a crude mixer?) to act as a remote speaker for a card, or is it more sophisticated than that.

That seems to be what it is. B8 goes to U25, a "14529." Google thinks it's a Ford window switch, so can't say exactly, but it's directly in front of the op-amp, and the 3-voice sound chip also feeds into it, so it's some kind of sound controller. Grab the technical reference manual from Oldskool if you don't already have it.

The EX/HX have B8 not connected to anything, so you would't get the pass-through audio there.

 

[blackepyon]

The... eccentricities, I'm running into are all part of the fun. I'm just getting amused at how the well of differences between these machines and regular old boring PCs doesn't seem to be showing any sign of bottoming out.

Likewise.
I find it interesting how Tandy managed to combine so many things to save space and costs. Such as mentioned above, how the EX/HX have the V-sync circuit coming out of the interrupt controller. The keyboard controller has pins controlling sound and floppy, and the parallel port controller manages some of the floppy controls as well. And the relationships change between each model.

 

[Eudimorphodon]

The keyboard controller has pins controlling sound and floppy, and the parallel port controller manages some of the floppy controls as well. And the relationships change between each model.

While working on my HX project I noticed all the weirdness hanging off the keyboard controller. Of course, to make it more fun the EX/HX technically have two chips you could call the "Keyboard Controller" onboard, the actual "keyboard controller" in the standard PC sense (but also moderates those other peripherals) and the 8048 MCU that actually *scans* the matrix keyboard, which is only connected to the other by a few lines. I haven't verified by looking at the other machines' tech manuals but I assume that everything downstream of the serial connection between the 8048 and the keyboard controller is roughly what you'd find in a normal detachable Tandy 1000 keyboard. But it's still interesting, or maybe it's actually *less* interesting because it's too conventional, that Tandy laid things out like that. I'm kind of surprised they didn't come up with a unified keyboard controller ASIC that directly scanned the matrix.

 

[RetroGaming Roundup]

Tandy was an insane place that made choices that amplified whatever Commodore did with things like the C64 disk drive crippling. They would spend a dollar to save a dime and figured the end user would never notice. Check out our recent podcast that features a talk by Paul Schreiber who tells what Tandy was like in those days. We will also be having one of the buyers from the 1000 era on soon.

 

[Eudimorphodon]

there seems to be an issue with DOS Kermit; a weird, funky issue that's going to force me to break out my second eBay V-20 to absolutely confirm it. Fun stuff!

So it seems like I've got me a head-scratcher. I went ahead and swapped a V-20 into the HX rig; as a result I was able to verify that ctmouse is indeed fixed by having a V-20... but Kermit wasn't. Kermit is behaving very badly on the HX with my integrated serial+IDE card, with transfers just bombing out, even after upgrading the CPU to the same that's been in the EX since I started using it. So apparently it's not the CPU like I thought.

I'm worried of course that there's some kind of issue with the card, but if I yank the stack out of the HX and stuff it into the EX Kermit works fine. (And this is running with the same boot drive, RAM configuration, everything.) Also, if I fire up ProComm with the same serial port speed/parity/etc settings that seems to also work fine on the HX. (And the mouse works... etc.) Now the *really* crazy thing: in one test I disabled both serial ports on the combo card (so it's just doing IDE duties), put my stand-alone card into the other slot jumpered to the same ports (COM1/COM2)... and that time it worked.

Apparently I need to find something else to exercise the serial port with. Some of how Kermit is behaving is almost making me wonder if there's some kind of BIOS difference between the machines, because on the HX the program sometimes blinks the screen when updating, which I don't see on the EX... but there's still that thing where it worked the one time with the stand-alone serial card. I really am starting to wonder if the HX does have "something" about it, a different version of some ASIC, that renders it a little more unstable than the EX, and for *some* reason it's smelling something strange about having the IDE and UARTs behind the same '245. (Which is the only difference between the unified card and the two separate ones in the prototype run.) But why does Procomm work?!

 

[blackepyon]

Tandy was an insane place that made choices that amplified whatever Commodore did with things like the C64 disk drive crippling. They would spend a dollar to save a dime and figured the end user would never notice. Check out our recent podcast that features a talk by Paul Schreiber who tells what Tandy was like in those days. We will also be having one of the buyers from the 1000 era on soon.

If you weren't the kind of person to notice the shortcuts taken, you probably weren't the kind of person to care. The only reason WE noticed, is because we've had to dive this deep into the hardware. Bottom line is that the customer got a functional machine for a reasonable price. THAT, I'd argue, drove the home PC market more than the IBM "personal" computer ever did (though I have a soft spot for old IBMs as well).

 

[blackepyon]

So, I got the PCBs from China. I haven't fully assembled the card yet, but I did enough to see how well the right-angle solder jobbie works.


I did one side of the backpanel section without any solder mask. Turns out I did get a couple measurements wrong, but this is why I submitted them as two separate files rather than having it as a break-off section. The vertical alignment of the holes is off by about .100 or so, and the holes for the PEM nuts need to be a hair larger. Once I get the next backpanel board run and confirm it works, I want to use this to create a template that other people could build their cards onto.

One note about using PEM nuts with CR4, don't over-tourque the bench vise, and make sure the PCB side has a smooth piece of metal as a shim, so you don't wreck the shiny bits. In a future iteration, I'll probably move the LED hole a bit further away from the holes, because it did crack slightly when I over-clamped it, leading me to shave off a little bit of the sides of the board to make it square again.

 

[bladamson]

Wow, that right-angle PCB jobbie looks a lot better than I was expecting!

Nice job.

 

[rkrenicki]

I am working with a vendor in China to have some proper 2x31 headers made up rather than piecing together 2 other sized headers, or getting a 2x32 and chopping off one row. Once I get the particulars worked out, I will share my vendor, or if anyone wants a few.. I am planning on ordering plenty of extras.

 

[eeguru]

I am working with a vendor in China to have some proper 2x31 headers made up rather than piecing together 2 other sized headers, or getting a 2x32 and chopping off one row. Once I get the particulars worked out, I will share my vendor, or if anyone wants a few.. I am planning on ordering plenty of extras.

Is there anyway they can do a proper double-tall male header with offset shroud like on the original RAM expansion Plus board? That way, whatever designs come out of this thread could be a proper replacement for the Plus RAM expansion allowing two more Plus boards to mount on-top.

 

[dJOS]

I am working with a vendor in China to have some proper 2x31 headers made up rather than piecing together 2 other sized headers, or getting a 2x32 and chopping off one row. Once I get the particulars worked out, I will share my vendor, or if anyone wants a few.. I am planning on ordering plenty of extras.

I’d be interested, however having been down this rabbit hole before and pouring a bunch of cash down the drain, I’d caution you to get a very small sample to test first. The batch I bought worked but where so tight that I nearly destroyed my Tandy ram expansion removing them. I ended up binning the lot.

PS I gave them the data sheet for the ones I had been using and they still got it wrong some how.

 

[rkrenicki]

Is there anyway they can do a proper double-tall male header with offset shroud like on the original RAM expansion Plus board? That way, whatever designs come out of this thread could be a proper replacement for the Plus RAM expansion allowing two more Plus boards to mount on-top.

I do not really have a need for such a connector, but if this works out okay, I can point you in their direction to see if you want to give them a try to make one.

I’d be interested, however having been down this rabbit hole before and pouring a bunch of cash down the drain, I’d caution you to get a very small sample to test first. The batch I bought worked but where so tight that I nearly destroyed my Tandy ram expansion removing them. I ended up binning the lot.

Was the internal contact the issue, or a problem with the hole diameter in the plastic housing? I am planning on 100 in the first order, but at the prices thusfar quoted.. I would not be "too" upset if they were unsuitable.

 

[dJOS]

Was the internal contact the issue, or a problem with the hole diameter in the plastic housing? I am planning on 100 in the first order, but at the prices thusfar quoted.. I would not be "too" upset if they were unsuitable.

The holes Seemed fine, the internal connectors were stiff to start with and just gripped way too tight.

I only wasted $100, but it was still frustrating.

 

[blackepyon]

Yeah, the 62-pin headers I've been getting from Digi-Key are too tight. The first couple that I ordered from a different manufacturer actually did fit properly, but they went out of stock. I'd definitely be interested if getting a handfull if you can get or find ones that actually fit properly.