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Thread: 8" hard sector floppy disk track format?

  1. #1

    Question 8" hard sector floppy disk track format?

    I am trying to get some information off a Zilog ZDS125 8" RIOS disks.

    They are standard 8" Single Density FM 128 or 132 bytes / sector, 32 sector, hard sectored disks.

    Does anyone know what the track format is for hard sectored disks and if any of the standard WD17xx chip sets can be programmed to format, read & write hard sectored disks? I know that most of the early hard sector controllers used programmed i/o to control the head load and stepper motors and tended to use a 74LS299 to handle the FM serial encode /decode.

    I have heard that some formats use standardish soft sector address and data marks and label the sectors in the normal way but use the hard sector hole to define the stat of the sector.

    I have a Z80 CP/M system with working 8" disk drive and 1791 based controller. But all my software uses it in soft sector either FM 128 byte SD x 26 sectors per track x 77 tracks or as MFM 256 byte DD mode.


    Thanks

    Peter

  2. #2
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    Ah, memories of the Zilog MCZ :"blue box".

    No, the track format is Zilog-specific. There's some documentation on the MCZ development system on bitsavers. It's very typical of early roll-your-own (pre LSI) floppy controllers. That is, the bit ordering within a byte is async comm order, not 3740 floppy order. The sector header is also unique. The CRC is pretty much standard, IIRC because the controller uses a standard Fairchild CRC chip.

    I converted a bunch of MCZ floppies a few years ago that used the WGBH closed-captioning software for Fox Home Video, which is how I managed to work the format out. I used a Catweasel card to get the raw data. One such floppy was the captioning for "Sun Valley Serenade" starring Sonja Henie...

    Note that the MCZ-2 is a different animal entirely and more-or-less uses the standard 3740 soft-sector encoding.

  3. #3

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    Quote Originally Posted by Chuck(G) View Post
    Ah, memories of the Zilog MCZ :"blue box".

    No, the track format is Zilog-specific. There's some documentation on the MCZ development system on bitsavers. It's very typical of early roll-your-own (pre LSI) floppy controllers. That is, the bit ordering within a byte is async comm order, not 3740 floppy order. The sector header is also unique. The CRC is pretty much standard, IIRC because the controller uses a standard Fairchild CRC chip.

    I converted a bunch of MCZ floppies a few years ago that used the WGBH closed-captioning software for Fox Home Video, which is how I managed to work the format out. I used a Catweasel card to get the raw data. One such floppy was the captioning for "Sun Valley Serenade" starring Sonja Henie...

    Note that the MCZ-2 is a different animal entirely and more-or-less uses the standard 3740 soft-sector encoding.
    Hopefully, the disk drive you have has a clock and data seperator ( only good for FM ). You can then use a synchronous USART like a 8251 to translate it into 8 byte chunks.
    I don't recall but you may need a oneshot or two to align and stretch the clock and data for the serial chip. Controlling the floppy is straight forward I/O work, using open collector and pullup resistors. ( note it is 5V levels so if you want to use an Arduino or other small micro, ( I like the "Blue Pill" with a stm32F103 ) it may only output 3.3v. For TTL, it needs to be 3.5V, minimum, up to 5V. You may need some level conversion.
    You can use USB with many of these boards but it will eat up a lot of your RAM and Flash, I recommend using a FTDI to convert the USB to serial while debugging. No sense making the project really hard. You can use one of the serial channels on the micro and avoid using the 8251 but that requires more uncertainty on completing the project.
    Dwight
    Last edited by Dwight Elvey; July 25th, 2018 at 10:45 PM.

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