Connecting a Gotek drive to the Olivetti M20

By Benjamin Eberhardt

Attaching a floppy drive emulator to the M20 can be an alternative to reading and writing original floppy disks. This enables one to share the same image between an M20 and an emulator. It's also an option to replace the original drive(s) with, in case movable components have failed and cannot be repaired.

One option for drive emulator, the counterpart to the Greaseweazle if you will, would be the Gotek floppy drive emulator with FlashFloppy firmware. This emulator would enable the M20 to use *img floppy images directly from a usb stick. Amigastore prepares the units and sells them already flashed and configured for your needs.

In order to connect the Gotek (or any other 320k PC drive), one has to make sure to disconnect the additional 12V power line from the M20. The M20 power connectors serve (5V, G, 12V, 12V) while PC connectors expect (5V, G, G, 12V). So the additional 12V line needs to be removed to make it PC compatible. Also avoid using the twist in the floppy cable for drive numbering, it does not seem to work on the M20, so both drives have to be connected to the un-twisted part of the data cable. Like the original M20 drives, also the Goteks have jumpers to define the drive order. In order to number the drives, these jumpers should be used.

The following config can be used to directly load MAME images:


     [::286720]
     file-layout = interleaved
     cyls = 35
     heads = 2
     interleave = 1
     secs = 16
     id=1
     tracks = 0.0 ## Boot cylinder, head 0
        bps = 128 ## Cylinder 0, head 0 has 128-byte sectors
        mode = fm
        img_bps = 256
     tracks = 0.1 ## Boot cylinder, head 1
        bps = 256 ## Cylinder 0, head 1 has 256-byte sectors
        mode = mfm
     tracks = 1-34 ## All other cylinders
        bps = 256
        mode = mfm

The config file needs to be placed into the root directory of a USB drive and named IMG.CFG. Image types are identified by their size. A standard M20 *.img file has 280 kiB or 286720 bytes. The config then specifies the logical M20 disk layout (35 cylinders, 2 heads, 16 sectors), as well as the mixed sector encodings (FM/ MFM). The Flashfloppy Gotek firmware also supports track padding as "img_bps" since v3.39 to support image files where the lower density FM data has been padded to realise a homogeneous sector size (This is a de-facto standard for M20 *.img images). One can read more about M20 floppy formats in the transfer and MAME articles

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