SPRHSTOP

    BIT#  15  14  13  12  11  10  09  08     07  06  05  04  03  02  01  00
SPRHWRM    x   x   x   x   x  v10 v9  v8     v7  v6  v5  v4  v3  v2  v1  v0


         SPRHWRM = Swaps the polarity of ARW* when the SPRHDAT comes
         out so that external devices can detect the RGA and put
         things into memory.  (ECS and later chips only)