Does anybody have the WD1793 data sheet?

If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
How to program the oric hardware (VIA, FDC, ...) is also welcome.
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ThomH
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Does anybody have the WD1793 data sheet?

Post by ThomH » Sun Nov 27, 2016 2:59 pm

I'm specifically having difficulty chasing up the logic behind the HLD (head load, presumably?) pin, which per the Microdisc schematic is wired directly to the drives' motor on. Is there a spin-up sequence as there is when the 1770 and 1772 changes the motor on line (i.e. enable signal, wait for six index pulses, then start the actual operation), or e.g. if I attempt a sector read from a standstill, does spin-up end up racing the index-pulse limit on declaring a record not found?

EDIT: in case it saves anybody the time checking, the widely available WD1770/2/3 data sheet does discuss the ways in which the 1773 varies from the 0/2 here — i.e. it substitutes side comparisons for motor logic in the relevant parts of the commands — and explains that the 1773 is fully software compatible with the 1793 but it's not pin compatible and doesn't even expose the same signals. So no content as to the '93's HLD.

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Chema
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Re: Does anybody have the WD1793 data sheet?

Post by Chema » Sun Nov 27, 2016 4:29 pm

Is this what you're looking for?

ThomH
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Re: Does anybody have the WD1793 data sheet?

Post by ThomH » Sun Nov 27, 2016 5:16 pm

Yes, perfect, thanks! So it's call and response: the 1793 sets the HLD output upon receiving a command and proceeds only once the HLT input is set, for which the Microdisc has an LS123 and another part whose number I can't quite make out but which I assume together amount to: wait a fixed period. HLD times out after a certain number of index holes so spin down is counted by that just as on a 1770/2 (albeit with a different duration). I'm a bit of an electronics dunce to be honest; I'm sure the number I can't quite read and therefore the net effect will be obvious once I look up the various things the other part number looks a bit like.

(aside: I guess the 1770 designers' intention was to allow interfaces with an external control for the motor as otherwise it's a bit weird that you can legitimately ask that it read a sector, but please do so without starting the motor, after which the chip will sit there for all time hoping that data will just arrive unless you interrupt it)

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iss
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Re: Does anybody have the WD1793 data sheet?

Post by iss » Thu Dec 01, 2016 1:52 pm

Hi ThomH,
during my work on floppy speed test I found newer and bigger pdf's here:
http://bitsavers.trailing-edge.com/pdf/westernDigital/
See:
FD179X_Data_Sheets_May80.pdf
FD179X_Application_Notes_Jun80.pdf

ThomH
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Re: Does anybody have the WD1793 data sheet?

Post by ThomH » Wed Dec 07, 2016 6:00 pm

Thanks! Those helped a lot. I won't bore you with the full litany of errors one could make by taking that "the WD1773 is 1793 compatible" statement too strictly but the absence of head loading logic is a lot of it.

For the Microdisc, I settled upon signalling HLT 7,653,333/8,000,000ths of a second after HLD transitions to active, and assuming that HLT is wired directly to the drive motor. I arrived at the number with only the vaguest of science: I compared the amount of time it took my emulator to perform a Sedoric DIR to a video of a real Microdisc doing the same that I cribbed from Youtube. Sedoric seems to perform a restore at the end of all disk accesses to move the heads back out to track 0 so, sure, there's some potential difference in exact starting rotation position but I should be close.

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Steve M
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Re: Does anybody have the WD1793 data sheet?

Post by Steve M » Mon Feb 13, 2017 8:29 pm

Do you need a chip? I have a lot of 8877 chips used in the Cumana. They aren't directly compatible and need some different capacitors or something but if you're stuck it might be possible to substitute.

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Re: Does anybody have the WD1793 data sheet?

Post by ThomH » Tue Feb 21, 2017 8:09 pm

Steve M wrote:Do you need a chip? I have a lot of 8877 chips used in the Cumana. They aren't directly compatible and need some different capacitors or something but if you're stuck it might be possible to substitute.
Oh, no, but thanks for the offer! It was merely academic interest pursuant of emulation. Sadly I don't have a real Oric, and am in a country where it would be even more difficult than usual to obtain one.

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