GOTEK

[Potholepete]

Decided to start a new topic on this subject as I am still having issues trying to get an image to read from the Gotek.

I got a new 28C64 eeprom and programmed it with an SDX image from Dave, added it to the SDX controller and I get exactly the same issues I was having with the existing ROM chips I have for the SDX. Basically after a time it comes back with disc error.

It may be that the image is not correct but I have used what I believe to be a non-cp/m 320k disk image (tried a few from Andy's site) and none of them work, the 640k ones don't either but with Dave's type 3 rom I expected them not to.

I have in total 6 disc based systems and none of them work with the original drives (some popped a cap others just are just broken) and I don't really want to use a floppy drive anymore when a 'working' Gotek is a much simpler and reliable solution.

Jim

[Martin A]

SO, the process here turned out to be:

Program the Gotek to the latest FlashFloppy 3.39.
Set the Gotek to Drive zero, no other jumpers set.
Unzip and copy the CF.CFG file below to the root of the USB stick
Copy any suatable sized 59k CPM bootable disc image to the USB stick, 320K in my case, file extension set to img.
E9 block of dip switches set to 5 and 8 on, the remainder off.
Connect the FDC board and Gotek with a PC 34 way IDC floppy cable. Red stripe to pin 34 at the FDC end. straight or twisted connection at the drive end doesn't matter.

Optional extra for type 07 drives (untested)
Set dip switch 6 to on

Optional extra to step the drive at 6ms if you don't plan putting the real 5 1/4 drive back in (tested)
Set dip switch 8 to off

Optional extras if your FDC board has faulty DMA circuitry. (Sadly also tested)
Replace 2x LS244 and 2x LS191 on the FDC board
Reprogram the FDX single boot rom to move the disc data buffers from the E9C0 to EB3F memory area to F580 to F6FF area.

Best advert for the MFX ever!

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Data connection

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FF.zip

Current FF.CFG file

(4.59 KiB) Downloaded 1309 times

[stephen_usher]

Were the original 74LS logic chips duff in some way?

[Martin A]

Were the original 74LS logic chips duff in some way?

They were. The MTX couldn't even boot with the FDC board plugged in until the LS244s were replaced. They're the chips at A1 and B1 on the board, the schematic shows that they buffer and isolate the 4 LS191 counters that store the floppy drive DMA address. They're only supposed to drive the bus when the DMA is active, B1 had one pin driving the bus high even when it was supposed to be inactive and floating. I replaced A1 as a precautionary measure**.

I've also had to replace 2 of the 4 counters, the chip at B3 wasn't counting and I swapped B2 out in an attempt to resolve a sticky A12 address line. That A12 line is still creating issues, so B2 might have been OK. The real source of that problem has turned out to be rather illusive.

It's actually possible to access the floppy drive without using DMA, in the same way that the SDX controller does. The current FDX single software build takes a different approach, I just moved the DMA buffer in ram to an address where A12 is high so that the problem is sidestepped for now!

**The replacement parts are HCT family, rather than LS, I wasn't sure having the different output characteristics driving each half of the bus was a good idea.

[stephen_usher]

HCT should be OK. They're only a little slower than TTL but use the same voltage triggering levels (approximately).

74LS244s are quite flaky at the best of times. I'm not sure if Memotech got somebad batches from TI but those and 273's seem to have been the chips which failed in my MTX500 in the late 80s.(Wow. I fixed that machine 4 years ago now!)

[Martin A]

Needing a bit of a clean, but otherwise complete.

The prevoulsy FDX single is now a FDX CPM twin using 2 x Flashfloppy modified Gotek drives.

The 5 1/4" bay adaptors were 3d printed as were the red end plates to match the function keys.

The 80 column display is courtesy of a custom CPLD design outputting 640x480 VGA in place of the 15KHz RGB that would have been historically accurate.

There was enough spare space on the PCB to fit 1Mb of Silicon Disc accesible using the original Memotech driver and a CFX style CF adaptor.

The minature USK keys have arrived

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The CF isn't currently supported by the Boot ROM. That's due to the lack of high memory, a loadable driver using a 54K CPM disc would be possible but there's no real need for it given the number of 640k disc images that will fit on the USB keys.

[gunrock]

Ooh, nice job. So you created a custom PCB just for this project, Martin? A proper PCB or a one-off, breadboard?

[Martin A]

Ooh, nice job. So you created a custom PCB just for this project, Martin? A proper PCB or a one-off, breadboard?

Derailling the Gotek thread a bit more , point to point soldered, one off, on matrix board. Pretty much the same way that CFX etc. were prototyped.

I soldered some 0.1" strips sockets into the pre-drilled holes on the FDX backplane as only 2 of the 6 potential slots have the edge connectors fitted. It means this board sits on the rails and not in them, but for a one off it's acceptable.

The neat side :)

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[1024MAK]

Derailed?

More like smashed through the terminus and just keep going…

Nice work

Mark

[stephen_usher]

That FDX (and machine) both need a bit of a deep clean!