ST506 and/or ST412 hard disk drives - CP/M

This is a discussion on ST506 and/or ST412 hard disk drives - CP/M ; On Jan 13, 10:05*am, MikeS wrote: > On Jan 12, 11:49*pm, glen herrmannsfeldt > wrote: > > > Just wondering, is the floppy side hard sectored? *The only reason > > I can think of for a PLL on the ...

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Thread: ST506 and/or ST412 hard disk drives

  1. Re: ST506 and/or ST412 hard disk drives

    On Jan 13, 10:05*am, MikeS wrote:
    > On Jan 12, 11:49*pm, glen herrmannsfeldt
    > wrote:
    >
    > > Just wondering, is the floppy side hard sectored? *The only reason
    > > I can think of for a PLL on the index line is for indexing sectors.
    > > I once thought about using a PLL on index to generate hard sector
    > > index pulses with a soft sector drive. *And yes, it would take a
    > > while to lock, so would need a continuous index.

    >
    > ---
    > Ummm... I don't follow you there; yes, as Andrew says the FD is hard
    > sectored, but how is that relevant to the HD index?
    >
    > Why would a PLL not be required for the HD? This would be news for the
    > designers of this controller, since as it happens the HD index signal
    > goes directly to a 4046 PLL, while the FD index first goes through a
    > discriminator to separate the sector pulses from the index pulse
    > before the two are multiplexed onto a common bus.
    >
    > mike
    >


    Oops...

    Sorry, Glen, I realized after I sent the above that I'd misunderstood;
    I thought you meant the PLL was required for the FD, but I think you
    meant that the PLL is required for the HD index in order for it to
    "emulate" a hard sector FD, which is indeed the case as far as I can
    tell.

    mike

  2. Re: ST506 and/or ST412 hard disk drives

    MikeS wrote:
    (snip)

    >>Why would a PLL not be required for the HD? This would be news for the
    >>designers of this controller, since as it happens the HD index signal
    >>goes directly to a 4046 PLL, while the FD index first goes through a
    >>discriminator to separate the sector pulses from the index pulse
    >>before the two are multiplexed onto a common bus.


    > Sorry, Glen, I realized after I sent the above that I'd misunderstood;
    > I thought you meant the PLL was required for the FD, but I think you
    > meant that the PLL is required for the HD index in order for it to
    > "emulate" a hard sector FD, which is indeed the case as far as I can
    > tell.


    Yes.

    The usual use for a PLL in disk controllers is the data separator
    running at the bit rate. That would sync up pretty fast.

    In a discussion a few months ago I had suggested using a PLL
    to emulate hard sector floppy disks using soft sector disks.
    I hadn't thought until that post why you would put a PLL on the
    index line, but then it occurred to me that it would allow the same
    fake hard sectoring.

    -- glen


  3. Re: ST506 and/or ST412 hard disk drives

    glen herrmannsfeldt writes:
    > In a discussion a few months ago I had suggested using a PLL
    > to emulate hard sector floppy disks using soft sector disks.
    > I hadn't thought until that post why you would put a PLL on the
    > index line, but then it occurred to me that it would allow the same
    > fake hard sectoring.
    >


    I had a computer that did exactly that -- the Decision disk controller
    for the DG Nova 1200 used 12-sector packs, but used a 16-sector
    format, using precisely a PLL. (I could be wrong about the 12 and 16
    -- could have been other numbers, it's been 20 years).

    --
    Lawrence Statton - lawrenabae@abaluon.abaom s/aba/c/g
    Computer software consists of only two components: ones and
    zeros, in roughly equal proportions. All that is required is to
    place them into the correct order.

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