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To: LARGE BUFFER
From: Mark Hovsepian
Subject:  DN20 Problems

     We have been getting an increasing number of calls  from  Field
Specialists  who  are  installing DECnet on TOPS20 machines with new
DN20s.  The most common complaint is that the  DN20  will  pass  all
diagnostics  flawlessly,  yet when the DECnet software is loaded the
front end will die, indicated with a DN20ST BUGINF.  In  most  cases
the   problem   is  caused  by  incorrect  switch  settings  on  the
microprocessor board and the line unit board.  The switch packs  are
located  on  various  places  on those two boards and should only be
corrected by Field Service Technicians.

     We  have  found  multiple  incorrect  sources  for  the  switch
settings in such places as Peripheral Handbooks, DMC11 manuals, DN2x
hardware fiche and even the labels on the expansion drawer.  Some of
the  addresses  and  vectors  are correct for certain diagnostic and
acceptance programs, but not for DECnet.  The following figures  are
the  only  ones that should ever be used for DN20 devices.  They are
hardwired in the MCB and settings  other  than  these  will  produce
various  undesirable  results  such  as  NETCON  errors  and  DN20ST
BUGINFs.

     KMC11s from 160540, Vector at 540

     DUP11s from 160300, Vector at 570

     DMC11s from 160740, Vector at 670

     The addressing/vector scheme follows increments of 10 for  each
additional line.