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-- KL MICROCODE BEWARE FILE --
July 1986






























COPYRIGHT (c) DIGITAL EQUIPMENT CORPORATION 1977,1978,
1979,1980,1981,1982,1983,1984,1986.  ALL RIGHTS RESERVED.


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.

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

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

KL MICROCODE BEWARE FILE -- V2.1(442)                           Page 2


KL-UCODE.BWR -- V2.1(442)
July 1986









1.0  KNOWN BUGS


     No known bugs.

     In testing this new microcode some poor programing concerning BLT
was  found  in  current  products.   Following  is an excerpt from the
DECsystem-10/DECSYSTEM-20 Processor Reference Manual:

     Should  an  interrupt  or  page  failure  occur  during  its
     execution,   the  BLT  stores  the  source  and  destination
     addresses for the next word in AC,  so  when  the  processor
     restarts  upon  the  return  to  the interrupted program, it
     actually resumes  at  the  correct  point  within  the  BLT.
     Therefore A and X must NOT address the same register as this
     would produce a different effective address calculation upon
     resumption;  and the instruction must NOT attempt to load an
     accumulator addressed either by A or  X  unless  it  is  the
     final location being loaded.



     [End of E442UC.RNM]