NAME   rev ADDR type chip Description
---------------------------------------------------------------------------
BPLHSTOP p 1D6  W    A    UHRES bit plane vertical stop

         +-------+---------+
         | BIT#  | Name    |
         +-------+---------+
         | 15    | BPLHWRM |
         | 14-11 | Unused  |
         | 10-0  | V10-V0  |
         +-------+---------+

         BPLHWRM = Swaps the polarity of ARW* when the BPLHDAT comes out so
         that external devices can detect the RGA and put things into memory
         (ECS and later versions).