No BMODE, CMODE      BMODE, CMODE
                     +-----+------+     +-----+------+
      R0 ---> area:  | 11  | chan |     | 11  | chan |
                     +-----+------+     +-----+------+
                     |     blk    |     |     blk    |
                     +------------+     +------------+
                     |     buf    |     |     buf    |
                     +------------+     +------------+
                     |    wcnt    |     |    wcnt    |
                     +------------+     +------------+
                     |     1      |     |mapping bits|
                     +------------+     +------------+
                                        |     1      |
                                        +------------+