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From: PERSHNG@YKTVMH3.BITNET ("John A. Pershing Jr.")
Newsgroups: comp.lang.asm370
Subject: CTCAs
Message-ID: <9001121543.AA26280@lilac.berkeley.edu>
Date: 12 Jan 90 14:04:53 GMT
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Reply-To: IBM 370 Assembly Programming Discussion List <ASM370%UCF1VM.bitnet@lilac.berkeley.edu>
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If you look at the NUCON mapping macro, you will notice that it provides
symbolic names for all of the low-storage locations.  It is considered
preferable to use these symbolic names, rather than absolute addresses.
Just remember to provide an appropriate USING pseudo-op in your assembler
routine:

         USING NUCON,0

Note, also, that CMS normally protects its data areas (which includes
Page Zero) with a storage key of x'F' and runs user programs under a PSW
key of x'E', so you will have a bit of trouble storing into these low-
storage locations (e.g., the CAW).  You can use the DMSKEY macro to ask
CMS to set the PSW key to x'0', or (a bit "safer") use the DMSEXS macro
to execute a single instruction (e.g., a store into the CAW) under a PSW
key of x'0'.

      John Pershing
      IBM Research, Yorktown Heights