USI:
  _modify:
    USISR:
      access: read-write
  USICR:
    _modify:
      USICLK:
        access: write-only
      USITC:
        access: write-only
    USIWM:
      _replace_enum:
        DISABLED:        [0, "All detectors disabled. Port pins operates as normal."]
        THREE_WIRE:      [1, "Three-wire mode. Uses DO, DI, and USCK pins."]
        TWO_WIRE_SLAVE:  [2, "Two-wire mode (Slave). Uses SDA (DI) and SCL (USCK) pins."]
        TWO_WIRE_MASTER: [3, "Two-wire mode (Master). Uses SDA and SCL pins."]
    USICS:
      NO_CLOCK: [0, "No Clock/Software clock strobe"]
      TC0:      [1, "Timer/Counter0 Compare Match"]
      EXT_POS:  [2, "External, positive edge"]
      EXT_NEG:  [3, "External, negative edge"]
  USISR:
    _modify:
      USIDC:
        access: read-only