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Coco FDC on a Dragon computer

T

TRS-Ian

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A few people have asked me over the years if I have a floppy disk controller (FDC) for the Tano Dragon 64, because apparently the TRS-80 Coco FDC doesn't work.

Come some people in the know tell me why it doesn't work and will an Eprom upgrade or other hardware mod make it work?

I currently have no Dragons to test, but don't want to re-invent the wheel if there is a known way to make a Coco FDC work on a Dragon.

Thanks in advance,

Ian.
 
It is indeed doable.
I have a self modified 26-3022 controller with a switchable dual Rom which works perfectly in both RSDOS mode and DragonDos.

All Dragon 32 and 64 machines carry the +/- 12V on the cartridge port so the 3022 operates correctly.

I can email you the Rom image ready to program or i can put together a how to for TRS8bit...
But it really is just a Rom replacement.

:)
 
What kind of mods have you made to the 3022?, only the double sized EPROM?
Never tried it; but does the 3022 work without -12V?. The Dragon slot connector doesn't provide this voltage (IIRC the Dragon 32 internal PSU doesn't not even generate it).
Posting a guide would be great tho :)
 
Thanks Corfiot,

So basically to summarise, the Dragon cartridge slot is electrically compatible with the Coco cart slot, and its just the contents of the Prom/Eprom which makes the difference. Sound like all Coco FDCs will work with the correct Eprom?

I've ordered me a Tano, so I'll try it out when that arrives.

Cheers,

Ian.
 
Hi guys

Yes it is fully cartridge slot compatible.
The 3022 only uses +12v and +5v so the lack of -12v is not a problem.
If i get a chance later i will take some photos of my 3022 whuch i use with both TRS80 Coco1,2 and 3 (Muktipak required for 2 and 3 due to missing +12v) and various Dragon 32's with no issues


TC :)
 
A true Dragon disk controller is different than a Coco controller. It addresses the disk controller chip differently. But, as long as your software does not try to bypass Disk BASIC and directly address the disk controller (like OS-9 or NitrOS-9), it should work with the disk controller.

Here is someone who has made a Dragon Compatible controller (It's in Spanish): http://hardware.speccy.org/temp/Dragon-1.html
 
Yep, I have two of these boards and they work great. They're a clone of the original DragonDOS cart, just a little smaller.

Easy to build; but tricky to calibrate if you don't have an oscilloscope.
 
I'll do one and let you know. The Corfiot explained how to do it. From memory it's like any 24-pin to 28-pin eprom upgrade: the 4 extra pins need to be wired somewhere else on the PCB, and one line (A13?) goes to a switch where High selects the top 8K and Low selects the bottom 8K...

Hope this helps,

Ian.
 
Hi guys.

The firmware Ian has on his site are the ones i sent him and are proved to work.
i dont have time today but will take my cart apart tomorrow and publish some pictures...and instructions.

It's an easy mod with no board mods or hookup wires if i remember.

:)
 
JonB said:
I wonder where I could get one of those boards from that the Spanish guy had made? He must have spares...
Click to expand...

I can ask him; but I think that he doesn't keep any spare PCB. He made a batch of PCBs some time ago; but after that it focused its efforts in the QL's QubIDE :rolleyes:
 
Ok I did one this evening and tested it on my Tano Dragon 64 and it works great. I used the 8K dratrs.rom burned to a 2764 Eprom and installed it in a 26-3129 CC FDC (a.k.a FD-500 FDC). Here is how I did it:

Burn dratrs.rom to a 2764
Bend out Pins 1,2,20,23,27,28
Remove the old RS-DOS Rom and insert the 2764 into the socket with pins 1,2,27,28 overhanging at the front.

Run the following wires:
2764 Pin 20 to a Gnd source (black wire in picture below)
2764 Pins 1,27,28 to a 5VDC source (red wire in the picture) to the positive side of the electro-cap which filters the 5VCD coming in from the cartridge port
2764 Pin 2 to socket underside pin 21 (A12 line, for those interested)
2764 Pin 23 to socket underside pin 18 (A11 ditto)

DSCN0383.jpgDSCN0384.jpg

Plug it in and try it out. Remember when formatting a diskette that DSKINI0 command has changed to DSKINIT

Discuss.

Ian.
 
So, absolutely no change in the DragonDOS ROM?, nice!

Now you only need to get a 27128, join and burn both rom and using a switch, wire A13 to +5V through a 4.7K resistor or to ground depending switch position. This way you'll switch between 8K banks.
 
Last edited:
Just made a switchable one, see photos below. Tested on my Coco 3 and Tano 64. Parts needed: 27128 Eprom, a switch, and some wires.

Here's how:

Burn dualfdc16k.rom to a 27128
Bend out Pins 1,2,20,23,26, 27,28
Remove the old RS-DOS Rom and insert the 27128 into the socket with pins 1,2,27,28 overhanging at the front.

Run the following wires:
27128 Pin 20 to a Gnd source (black wire in picture below - this time I wired it to Pin 14 (Gnd) on the Eprom)
27128 Pins 1,27,28 to a 5VDC source (red wire in the picture) to the positive side of the electro-cap which filters the 5VCD coming in from the cartridge port
27128 Pin 2 to socket underside pin 21 (A12 line, for those interested)
27128 Pin 23 to socket underside pin 18 (A11 ditto)
Mount a small switch in the case (see picture, below)
27128 Pin 26 to the centre post of the switch
Run wires from the other two posts on the switch - one to Gnd, one to 5VDC
(see picture, below)

DSCN0385.jpgDSCN0386.jpg

The place I put the switch was chosen because whether the FDC is plugged into a Coco 1,2,3 or Dragon, or a MPI its easy to reach (if needed) but sufficiently out of the way so you won't accidently knock it to the other DOS in the middle of a 5 hour programming session.

Discuss.

Ian.
 
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Hi Ian

i notice you didnt use the switching scheme i described to you...
I wouldnt advise connecting 5v and 0v directly either side of the switch as you are prone to shorting your PSU if the switch fails.

Run a 4k7 resistor between 5v and pin 26...then run a length of wife to a simple SPST on off switch from pin 26 and any ground point.

I appreciate Ian describing the mods here as i havent had the time to photograph and document it myself...

Please note the Dragon firmware is NOT from Dragon Data, it is a modified version to allow the DOS to work on the CoCo's different FDC controller.

Regards
TC :)
 
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