Subject: RXV21 question

From: "Stuart Johnson" <[email-masked]>
Date: Sat Apr 5 23:22:01 2003

OK, this may be obvious to the experts here, but I haven't a clue: can a DEC
RXV21 RX01 / RX02 floppy controller be used with non-DEC floppy drives, using
the standard DEC RT11 driver? By non-DEC I mean ordinary SSSD or SSDD Shugart,
Siemens, or Qume 8" floppy drives.

I recently saw a project where someone uses a Linux PC to act as a RX02 floppy
for a PDP-11 system. That got me thinking: if I can use the RXV21 with foreign
floppy drives, I already have a pair of 8" floppy drives that I could use.
This would be VERY handy and save me some $$$.

OK experts, what is the verdict?

Thanks in advance!
Stuart Johnson

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From: [email-masked] (Tony Duell)
Date: Sun Apr 6 13:06:14 2003

> Siemens, or Qume 8" floppy drives.

Anything is _possible_ (apart from ski-ing through a revolving door :-)), 
but it may not be easy. And using an RX211 or RXV21 or RX8 or ... with 
normal drives is certainly not easy.

The reason is that these cards are _not_ floppy controllers. They're bus 
interfaces between Unibus/Qbus/Omnibus and a serial link to the drive. 
The actual controller is inside the drive chassis -- a board of AMD29xx 
bit-slice chips in the RX02 and a board of TTL + microcode PROMs in the 
RX01. This controller is responsible for positioning the heads, finding 
sectors, doing the CRC, and so on.

Third-party contollers (mostly Qbus) that linked SA800 drives to DEC 
machines had a fair amount of logic on the card, often including a pair 
of 2901 ALUs and a 2910 sequencer.

-tony

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From: Ethan Dicks <[email-masked]>
Date: Sun Apr 6 23:22:00 2003

> of 2901 ALUs and a 2910 sequencer.

I have one of those - came in a DataRAM box with a DEC CPU and 3rd party
peripherals (RAM, serial, DQ614, watchdog board).  Nice cabinet.  Room
for two Tandon TM8xx drives up front (I have one) and a FH 5.25" ST-506
drive buried inside - all before DEC released the BA23, so an embedded
disk was somewhat novel.

I'll have to see what's on the floppy board.  I remember attempting to
use it, back in the day.  We were trying to format blanks in it with a
low success rate (c. 1985).  Turns out there was a cold solder joint
on the TM8xx power connector that finally lifted clean off.  I tacked
it back down and it stopped burping.

-ethan