NAME   rev ADDR type chip Description
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BLTALWM    046  W    A    Blitter last word mask for source A

         The patterns in these two registers (see also: BLTAFWM)
         are "anded" with the first and last words of each line of data
         from Source A into the Blitter. A zero in any bit overrides
         data from Source A. These registers should be set to all
         "ones" for fill mode or for line drawing mode.