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DX20LD -- REVISION 4(5)

November 1980















                        COPYRIGHT (C) 1980 BY

                DIGITAL EQUIPMENT CORPORATION, MAYNARD, MASS.

        THIS SOFTWARE IS FURNISHED UNDER A LICENSE FOR  USE  ONLY  ON  A
        SINGLE COMPUTER SYSTEM AND MAY BE COPIED ONLY WITH THE INCLUSION
        OF THE ABOVE COPYRIGHT NOTICE.   THIS  SOFTWARE,  OR  ANY  OTHER
        COPIES  THEREOF, MAY NOT BE PROVIDED OR OTHERWISE MADE AVAILABLE
        TO ANY OTHER PERSON EXCEPT FOR USE ON SUCH SYSTEM AND TO ONE WHO
        AGREES  TO  THESE  LICENSE TERMS.  TITLE TO AND OWNERSHIP OF THE
        SOFTWARE  SHALL  AT   ALL  TIMES  REMAIN  IN  DIGITAL  EQUIPMENT
        CORPORATION.

        THE INFORMATION IN THIS DOCUMENT IS SUBJECT  TO  CHANGE  WITHOUT
        NOTICE  AND  SHOULD  NOT BE CONSTRUED AS A COMMITMENT BY DIGITAL
        EQUIPMENT CORPORATION.

        DIGITAL EQUIPMENT CORPORATION ASSUMES NO  RESPONSIBILITY FOR THE
        USE  OR  RELIABILITY  OF  ITS SOFTWARE IN EQUIPMENT WHICH IS NOT
        SUPPLIED BY DIGITAL EQUIPMENT CORPORATION.

                                                                  Page 2


The DX20 is a microcoded device that must have its  microcode  down-line
loaded.   Any  DX20's  on  a  system  are  automatically  loaded by BOOT
whenever TOPS20 is manually loaded by the operator.  Sometimes, however,
it  is  desireable to manually reload the DX20 microcode while TOPS20 is
up and running.  The DX20LD program is designed to perform  this  manual
reload of the DX20 microcode.

The DX20 comes in two basic types:

     1.   1 for TU70-series tape drives (type DX20A)

     2.   1 for RP20 disk drives (type DX20B).

(Note that the type, channel # and unit # of each DX20 are reported
on the CTY by BOOT when it reloads the DX20's during a manual restart
of TOPS-20.  During an auto-restart of TOPS-20, only DX20B's are reloaded.)

Corresponding to these two types of DX20 are two types of microcode:

     1.   TU70-series microcode:        in file DXMCA.ADX

     2.   RP20 microcode:               in file DXMCE.ADX


If your system has only one DX20 on it (or only  one  of  each  type  of
DX20),  then  you  need  only  specify the appropriate microcode file as
follows (assuming you have a TU70-series DX20):

     @DX20LD
     File: DXMCA.ADX<ret>

If you have more than 1 of the same type  DX20  (2  TU70-series  DX20's,
say),  then  you  must specify the channel number and the DX20 number of
the particular DX20 you want to reload:

     @DX20LD
     File: DXMCA.ADX/D:12<ret>

The /D switch, shown in the above example is of the  form  /D:mn,  where
"m"  is  the  channel number (RH20 controller #) and "n" is the DX20 number
of the DX20 that should be reloaded.

Ordinarily, the filename is sufficient to identify to DX20LD,  the  type
of  DX20  (tape  or  disk)  to  be  reloaded.   Any filename of the form
"DXMCAxxxxxxxx.ADX" indicates microcode for a TU70-series DX20 while any
filename of the form "DXMCExxxxxxxx.ADX" indicates microcode for an RP20
DX20.  If, for some reason, it is necessary to  load  microcode  from  a
file  whose  name  does  not  follow  these  conventions,  then  /T (for
TU70-series tape drives) or /R (for RP20 disk drives) may be  specified.
(Be careful, as it is possible to force DX20LD to load the wrong type of
microcode for a given DX20.)

                                                                  Page 3


File summary:

DXMCA.ADX               TU70-series DX20's (DX20A)
DXMCE.ADX               RP20 DX20's (DX20B)

Switch summary:

/D:mn           Load microcode for channel "m", DX20 "n"
/T              Load microcode only for TU70-series DX20's
/R              Load microcode only for RP20 DX20's


When to reload the DX20:


     1.  When the DX20 microcode  stops  -  giving  BUGCHK's
         DXBDMI or DXBDIE, or BUGINF DX2HLT.

     2.  Power-fail restart caused by line  interference  or
         power spikes.

     3.  Someone has manually powered-down the DX20.

     4.  Auto-reload  of  operating  system  (necessary   to
         reload  only  DX20A's  -  BOOT  will  automatically
         reload DX20B's).


When not to reload the DX20:


     1.  Never make a practice of reloading a DX20 while  it
         is  currently  performing IO transfers - there is a
         posibility of writing random  data  to  a  tape  or
         disk.  In the latter case you could cause damage to
         the disk structure.