7.3.5 DRP (Dual-Role Port)

A Dual-Role port functions as both a DFP and a UFP. The TUSB422 supports DRP either autonomously or manually. In autonomous DRP mode, the TUSB422 state machine toggles between UFP (Rd) and DFP (Rp) on both its CC pins. Autonomous DRP is enabled by programming Role Control register to 0x4A and writing Looking4Connection command to the Command register. Manual mode is under complete control of external processor. External processor must toggle between writing 0x0A and 0x05 to Role Control register at interval defined by Type-C specification summarized in Table 2.

The following steps are for initialization of the TUSB422 for DRP operation.

1. Upon TUSB422 power-up, the Power Status flag in Alert Register should get set indicating TUSB422 is initialized. When set, this flag will cause the INT_N pin to be assert low.
2. SW read the Alert Registers to determine reason for INT_N assertion. The expectation is Power Status bit (Reg10h bit 1) is set.
3. SW read Power Status register and notice that TCPC_INIT_STATUS flag is cleared. This indicates TUSB422 is ready.
4. SW clear Power Status bit in Alert register by writing a 1’b1 to the bit.
5. Program the TUSB422 to present Rd on both CC pins. This is done by writing 0x4A to the Role Control register
6. Write Look4Connection command to the Command register.
7. The TUSB422 now presents Rd on both Rp pins and look for a connection.

The TUSB422 autonomously toggles between Rd and Rp according to the setting of the CC General Control register. If a value other than default value is desired, then CC General control should be programmed to desired value before performing Step 6.