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Thread: 3174 Microcode imaging

  1. #1

    Default 3174 Microcode imaging

    I made an interesting discovery today. After taking another look at the pinout for the 2.4 meg drive, I decided to see what happened when I pulled pin 2 low while the disk was spinning. The drive went from 360 rpm to 180 rpm, which I confirmed with my scope. Additionally, the read data waveform seemed to change a bit but I can't really quantify this.
    Anyway I decided to try imaging the disk in this mode using a pentium machine with the HxC floppy software. With pin 2 jumpered to ground the program successfully read 30 sectors per track with the exception of track 0 side 0 which we had already determined to be formatted normally. In the end I have a 2,441,216 byte image file.
    I tried switching the jumper after the program read track 0 side 0 but the program would only read 15 sectors for the subsequent tracks.

    I suppose with this knowledge, someone could hack up a better solution for reading and emulating these disks.

    edit: I should also mention that I found several EBCDIC strings in the image.

  2. #2
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    That pretty much agrees with my suspicion--Weltec, back in the day (ca. 1986) offered a rather unsuccessful drive that allowed the use of 1.2MB floppies on a stock PC-XT by switching the spindle speed from 300 (for 360K media) to 180 (for 1.2M media). It was fabulously unsuccessful, lasting less than a year. The drive was a 96 tpi unit, so it had the usual liabilities of the AT double-stepped 360K floppies, though Weltec did offer software to do single-stepped 360K media. Where it really fell down was reading 1.2M media. Recall that the current induced in a disk read head is proportional to the linear speed of the media. At 180 RPM, it just didn't work well. Weltec dropped the HD media claim and just sold the thing as a 360K/720K unit. Good times.

    So the idea isn't dead. Running your drive at 180 RPM should render it compatible with any PC high-density imaging utility. No need for special hardware.

    Emulation may be a problem as the track at 2.4MB is twice as long as a standard 1.2MB one; The usual emulation hardware (e.g. Gotek) may not have enough RAM to do the job.

  3. #3
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    Quote Originally Posted by Chuck(G) View Post
    That pretty much agrees with my suspicion--Weltec, back in the day (ca. 1986) offered a rather unsuccessful drive that allowed the use of 1.2MB floppies on a stock PC-XT by switching the spindle speed from 300 (for 360K media) to 180 (for 1.2M media). It was fabulously unsuccessful, lasting less than a year. The drive was a 96 tpi unit, so it had the usual liabilities of the AT double-stepped 360K floppies, though Weltec did offer software to do single-stepped 360K media. Where it really fell down was reading 1.2M media. Recall that the current induced in a disk read head is proportional to the linear speed of the media. At 180 RPM, it just didn't work well. Weltec dropped the HD media claim and just sold the thing as a 360K/720K unit. Good times.

    So the idea isn't dead. Running your drive at 180 RPM should render it compatible with any PC high-density imaging utility. No need for special hardware.

    Emulation may be a problem as the track at 2.4MB is twice as long as a standard 1.2MB one; The usual emulation hardware (e.g. Gotek) may not have enough RAM to do the job.
    what we still don't know is how the drive knows its a 2.44m disk.....
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

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