Need help with CDC Sabre 9720-850 and Xylogics 753 on Sun 4/280

[Michael Maciolek]

I offer this as a general posting so it can go on record in the archives
in case anyone else needs the same information.

Relevant to the original poster, who wants to run this on a 4/280 - we
haven't tried it on a Sun-4, only on four Sun-3/280s.  I see no reason why
this should fail to work on a 4.

Note that the controller settings and the drive settings are quite
independent of each other.  I was using the same drive settings when our
Sabres were connected to xy451 controllers.

The disk:

1. The CDC 9720 Sabre 850 megabyte drive has two (known to me) different
control-logic boards, which you can tell apart by looking at the sector
switces on top of the drive.

The older style has three 6-position DIP switches, the newer style has two
10-position switches.  The settings we use will configure the drive for 69
sectors of 594 bytes each.

WARNING! The Xylogics 753 guide claims that a minimum of 600 bytes per
sector are required.  This configuration works for us, and we haven't
crashed a disk or lost a file yet, but we assume no responsibility for
others' use of these settings.

Our sector switches are set like this:

                                 closed
                        +------++------++------+
                        |     x||x x   ||xx    |
(3 x 6)        o o o o  |123456||123456||123456|
                        |xxxxx || x xxx||  xxxx|
               ^^^^^^^  +------++------++------+
               |||||||            open
         (status LEDs)


                                 closed
                        +----------+ +----------+
                        |xxxx x  x | |xxx  xxxxx|
(2 x 10)       o o o o  |123456789a| |123456789a|
                        |    x xx x| |   xx     |
               ^^^^^^^  +----------+ +----------+
               |||||||            open
         (status LEDs)




The controller:


Oriented component-side up, P1 and P2 connectors at the bottom:


  xxxxxxxxxxxxx      xxxxx     xxxxx     xxxxx     xxxxx
+---------------------------------------------------------+
|                                                         |
|                                                         |
|                                                         |
|                                                         |
|                                                         |
|                          :jG                            |
|                                                         |
|                                                         |
|                                         jE     ......   |
|                                         ::     ......   |
|                                 ::::::::::::   ......   |
|                                     jA         ......   |
|                                                jBjCjD   |
|                                                         |
+---------------------------------------------------------+
  #####################             #####################        


jA selects the address, which should be ee80 for xdc0.

   It should be set like this:   . . . # . . . # . # # #
                                 . . . # . . . # . # # #
                                           jA

jB thru jD determine the bus request and bus grant levels.

   They should be set like this:      . . . ### .
                                      . . . ### .
                                      . . . ### .
                                      ### ### ###
                                      jB  jC  jD


jE modifies the behavior of the controller's maintenance
   mode and self-test operation.  It should be set like this:

                                  jE
                                  # .
                                  # .


jG is "proprietary to Xylogics" and should be IN.


When you run "format", tell it 594 bytes per sector, 68 sectors/track, 15
heads, 1379 data cylinders and 2 alternate cylinders.  I think it will
also prompt for "drive type", (if you are mixing different types of disk
on the SAME controller, you will want to assign unique drive types to each
drive before you format it) and "disk rpm" (3600).

This configuration allows one slip-sector per track, which ought to be
fine for any normal application.  You will have about 687 megabytes of
space after formatting, before creating filesystems.  (my definition of
megabyte is 1024x1024 bytes, by the way)


Good luck!

Michael Maciolek		mikem at juliet.ll.mit.edu 	(preferred)
G43 SysAdmin			mikem at xn.ll.mit.edu
MIT/Lincoln Laboratory