Early 3.5" Floppy Drives

Chuck Guzis cclist at sydex.com
Thu Dec 15 15:29:46 CST 2005

n 12/15/2005 at 3:21 PM Allison wrote:

>>Subject: RE: Early 3.5" Floppy Drives
>>   From: "Chuck Guzis" <cclist at sydex.com>
>>   Date: Thu, 15 Dec 2005 11:30:29 -0800
>>     To: cctalk at classiccmp.org
>>On 12/15/2005 at 1:18 PM Allison wrote:
>>>;) your assumption is double density.  8" SSSD is not that fast.
>>>I never said formats were the same or even dive interface only that
>>>the data rates fly.
>>Nope.  I'm just going by the 765 data sheet:
>>"Pin 19 - CLK - Single-phase 8 MHz (or 4 MHz for mini-floppies)
>>IOW, if you supported 3.5  DD (or SD) floppies, you weren't going to be
>>able to do an A1 8" floppy without changing the clock.
>;)  You know not the part you speak of.  Question, what it that clock used

>for?  Hint data rates are NOT tied to it.  

...unless you count WRITING :) -- or is it your contention that FDC's not
be capable of writing data?.  AFAIK, neither NEC nor its licensees has
changed the relationship between the write clock and the 4 or 8 MHz clock

Could a 765 running off of a 4MHz clock, given the proper data separator
read 8" A1 diskettes?  Maybe, but there are some other things tied to the
clock that might have an effect, such as the length of the VCO sync-up
period.  Could it write or format them?  No way--it's just not built that

>Not even close 765 is a wholly differnt animal.  The Read operation needs 
>RDW and the write must have WC.  Both are independent of the chipclock.

Where be this WC pin on the 765 you speak of?  I don't see it.  Heck, I
don't see it on the 179x, either.

IMOHO, I note that it's the newer smaller drives, not the 8" drives that
step faster, so, using your logic, it'd be the 8" drives, not the 5.25"
that needed the slower clock.


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