This is the Tandy 1000 20MB Disk System.
Most Tandy machines didn't really have the space to have an internal hard drive. Even if they did, the original Tandy 1000 had a 54 watt power supply, so plugging a hard drive in was likely to make it fall over.
This solved both problems - this external chassis has its own power supply.
There are some prerequisites. First, you need a memory expansion - using the hard drive requires a minimum of 256K of RAM.
Secondly, your memory expansion needs to have the optional 8237 DMA controller chip on it. Like the PCjr it largely copied, the Tandy 1000 has no DMA controller by default.
Finally, you need the Tandy Hard Disk Controller Card.
The controller card itself is your standard MFM controller, using the same Xebec hard disk controller design seen in the IBM XT hard disk controller. This controller uses a Z80 for low level disk communication, and has two ROM chips, one for the x86 hard disk controller expansion BIOS, and the other for the Z80's controller firmware.
This controller exclusively operates via DMA.
This drive, unfortunately, was sold to me without the controller card, and the controllers and the custom cabling are quite rare and expensive.
So we may sadly never discover what is on this drive.
I don't know if these have been scanned before. If they haven't or if the existing scans kind of suck, don't worry I will scan them.
I want to show you this hilarious bit in the 20-Meg Disk System manual:
Your hard disk contains no more than 24 flawed tracks.
A brand new hard drive can have a little bad sectors, as a treat.
Did our proud Tandy owner dutifully record these in the manual on page 4, in the table provided?
Yes, yes they did.
Gotta love me some provenance
I have everything I need to try to fire this thing up, except the correct BIOS version. :(
It says here I should contact my local Radio Shack to inquire about a ROM upgrade, but for some reason they aren't picking up the phone...
Two screws release the floppy drive tray assembly, and a quick power disconnect allows us to lift the assembly straight up and out of the system.
If we see two chips in U9 and U10, we're basically screwed for the time being.
If there's only one chip in U9, we should be able to use one of them fancy new OneRom Fire 28 chips to replace it.
I need to verify what model of EPROM I need to emulate here, because the part # of the ROM is basically useless, being a one-off internal Motorola part number for a mask ROM.
A 27128 EEPROM may do, but we need to ensure pin 27 is high because that is the active low /PGM pin and we don't want it just programming itself all the time. Probably not ideal.
It's not like Tandy was going to just add a convenient set of pads so we can replace the mask rom with a 27128.
Oh wait, they did actually do that.
This is a OneROM Fire 28. This little guy costs about ten quid, and has a RP2350 microprocessor on it that's probably 500x faster than the entire system it is going into just to pretend to be a particular ROM chip.
I'm a bit concerned about clearance, so I'm going to leave off the 2x5 header for now, but if you do have the room for that, you can put multiple ROMs on this thing and easily switch them out.
Thanks to the magic of WebUSB, a standard that probably shouldn't exist, we can even flash this thing with a web browser. How neat is that.
I like the gray and yellow UI. It's kind of like Grindr for ROM chips
as an emulator developer, I must assure you that I legally dumped this ROM myself from .. uh, the other Tandy 1000 I have and am not just using for some reason.
honest
what's the situation with commodore 64 ROMs anyway now? did perifractic release that shit? do we still need to invade Italy? I've lost track.
I hope that was sorted out because you can see this thing shipped with the c64 kernal ROM on it.
well fluff my fanny I guess we just discovered the Tandy 1.02 BIOS is incompatible with the original 1000.
Okay, 1.01 begrudingly it is.
success!
..okay, this was kind of a case of me kicking myself in the ass for two hours.
I use 1.02 in my own emulator when emulating the Tandy 1000. It works fine. Apparently it shouldn't.
Another one of those fun cases when your emulator is inaccurate enough that something that shouldn't work, does.
The OneROM is a slick product, well designed and fairly easy to use, although the UI of the OneROM studio is a bit confusing, so I ended up just using the web page interface.
4.8/5.0 stars. Would flash again.
Check it out here: https://onerom.org/
@gloriouscow @michaelborthwick
I think he meant: how do you make a hardware device which is compatible with both 28 pin AND 40 pin ROMs?
And that is well explained in the linked video.
I love the idea: I had a battery backed RAM in my BBC micro ROM socket to use all the disk based ROM programs.
gloriouscow
michaelborthwick
Axel