MS_code_conventions


 During a primary address cycle, the two LSBs  of  the  first
 register  operand  field  are  used  to  select the MS code.
 Symbols for the MS codes have been  assigned  (globally)  as
 follows:

 D==0     ; data space for device
 C==1     ; CSR space for device


 DM==2    ; data space for broadcast
 CM==3    ; CSR space for broadcast

 Thus an instruction to read Fastbus CSR space might be written as
 DM                      ; Data memory
 SLOT:   DC      4       ; Primary address of module = 4
         DC      0       ; secondary address =0
         DC      VAL_CSR0; address of location to be written to
 VAL_CSR0:DS     1       ; reserve space
 PM                      ; Program memory
         FR      C,SLOT  ; FASTBUS instruction to read CSR 0

 Note  that  the  standard  FASTBUS  call  to  perform   this
 operation  (e.g.   in FORTRAN) is "CALL FRC(....)".  The IBM
 assembler  instruction  looks  like  an  "FRC"   instruction
 (ignoring  the  space  between  the  'FR'  and  the  'C'  ).
 Similarly,  the  "CALL  FRD"  equivalent  instruction  would
 appear in IBM assembler as

      FR D,SLOT

 and the broadcast read instruction "CALL FRCM" would be

      FR CM,BROAD

 It is requested that all BNL787 SSP programmers keep to this
 convention for ease of reading other people's code.

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