USB Command Code
| RESERVED | Reserved. Read value is undefined, only zero should be written. |
| CMD_PHASE | The command phase: 1 (WRITE): Write 2 (READ): Read 5 (COMMAND): Command |
| CMD_CODE_WDATA | This is a multi-purpose field. When CMD_PHASE is Command or Read, this field contains the code for the command (CMD_CODE). When CMD_PHASE is Write, this field contains the command write data (CMD_WDATA). |
| RESERVED | Reserved. Read value is undefined, only zero should be written. |