Subject: Re: Dec PRo help
From: [email-masked] (Kurt Wampler)
Date: Sat, 17 Apr 1993 22:00:33 GMT
Newsgroups: comp.sys.dec.micro

[email-masked] (Dave Clarke x8048) writes:

>hi, 
>	I want to add a further RX50 drive to my PRO350 to get DZ3:,DZ4:.
>But, I have a problem that I cannot make the drive online to the PO/S
>V3.2 operating system. I have tried the J17 drive select plug in both drives
>(DZ1:,DZ2:, one pair and DZ3:,DZ4: the other); But each time the drive acting
>as DZ1/2 works and DZ3/4 do not become online. Does anyone out there know
>what I have to change or set to make these drives online. Further to this I
>will be wanting to add another hard disk to a PRO380, and think that I will
>have the same problem as the RX50's.
>
>			PLEASE HELP,
>			many thanks,
>				Dave.

Dave -

I dug out my PRO300 Technical Manual and studied it a little in an attempt
to answer your question.  The documentation is inconsistent.  On p.10-36
there's a table that purports to describe how the select pins affect the
drive.  It states:

DRIVE SEL3 L  Selects drive side B if J17 installed
DRIVE SEL0 L  Selects drive side A if J17 not installed
DRIVE SEL1 L  Selects drive side B if J17 not installed
DRIVE SEL2 L  Selects drive side A if J17 installed

I'm not sure what this means, since the RX50 drive records one side only of
each diskette, and only has a read/write head on that side of the diskette.

The chapter on the RX50 controller adds to the confusion.  Section 9.3.3.2
on p.9-14 states:
"The microprocessor generates four signals for selecting an RX50 drive:
UNIT 0, DRIVE 0 and SEL EN, and SIDE.  The SIDE signal is reserved for future
use.  A unit selection decoder decodes the remaining signals and generates the
drive select signals, SEL0 L, SEL1 L, SEL2 L, or SEL3 L.  Table 9-4 shows
this conversion."

Table 9-4 Drive Select Signal Conversion
Asserted Control Signals         Asserted Selects
UNIT0 H   DRIVE0 H   SEL EN L    0    1    2    3
X         X          No          No   No   No   No
No        No         Yes         No   No   No   Yes
Yes       No         Yes         No   No   Yes  No
No        Yes        Yes         No   Yes  No   No
Yes       Yes        Yes         Yes  No   No   No

It seems like there was some confusion among the designers about the exact
definitions of "drive" "unit" and "side".  It's as though there was a debate
about whether to use the signals to select 4 different diskettes (A,B,C,D) or
to at some later time support double-sided diskettes.

Also, the chapter on the RX50 controller states on p.9-2:
"The controller interfaces *one* RX50 dual diskette drive to the host
processor [to] provide 819,200 bytes of storage."

Maybe my book's out-of-date and they cleaned up these inconsistencies in a
later version...

P/OS 3.2, however, does have those device definitions for DZ1, DZ2, DZ3, and
DZ4, implying that they did support a dual-RX50 configuration.  I wonder what
would happen if you just installed J17 on a single RX50 unit and booted up
P/OS.  Would it show up as DZ3/DZ4 online?

Conclusion:  the documentation I have is not sufficient to answer your question.
But perhaps the above information is of use.  Good luck!

Kurt Wampler
[email-masked]