No BMODE, CMODE      BMODE, CMODE
                     +-----+------+     +-----+------+
      R0 ---> area:  | 10  | chan |     | 10  | chan |
                     +-----+------+     +-----+------+
                     |    blk     |     |    blk     |
                     +------------+     +------------+
                     |    buf     |     |    buf     |
                     +------------+     +------------+
                     |    wcnt    |     |    wcnt    |
                     +------------+     +------------+
                     |    crtn    |     |mapping bits|
                     +------------+     +------------+
                                        |    crtn    |
                                        +------------+