NAME   rev ADDR type chip Description
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VPOSR  p 004   R    A   Read vert most sig. bits (and frame flop)
VPOSW    02A   W    A   Write most sig. bits (and frame flop)


 BIT#  15  14  13  12  11  10  09  08     07  06  05  04  03  02  01  00
 USE LOF   I6  I5  I4  I3  I2  I1  I0 LOL --  --  --  --  --  V10 V9  V8

         LOF = Long frame(auto toggle control bit in BPLCON0)

         I0-I6 Chip identitication:

         8361 (Regular) or 8370 (Fat) (Agnus-ntsc) = 10
         8367 (Pal) or 8371 (Fat-Pal) (Agnus-pal)  = 00
         8372 (Fat-hr) (agnushr),thru rev4         = 20 Pal, 30 NTSC
         8372 (Fat-hr) (agnushr),rev 5             = 22 Pal, 31 NTSC
         8374 (Alice) thru rev 2                   = 22 Pal, 32 NTSC
         8374 (Alice) rev 3 thru rev 4             = 23 Pal, 33 NTSC

         LOL = Long line bit. When low, it indicates short raster line.
         v9,10 -- hires chips only (20,30 identifiers)