7.3.4 UFP (Upstream Facing Port)
A UFP is a port that will present Rd on its CC pins and sink VBUS. The TUSB422 functions as a UFP by programming the Role Control register to 0x0A. This will cause TUSB422 to present a Rd on both CC pins.
The following steps are for initialization of the TUSB422 for DFP operation.
- 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.
- SW read the Alert Registers to determine reason for INT_N assertion. The expectation is Power Status bit (Reg10h bit 1) is set.
- SW read Power Status register and notice that TCPC_INIT_STATUS flag is cleared. This indicates TUSB422 is ready.
- SW clear Power Status bit in Alert register by writing a 1’b1 to the bit.
- Program the TUSB422 to present Rd on both CC pins. This is done by writing 0x0A to the Role Control register
- Write Look4Connection command to the Command register.
- The TUSB422 now presents Rd on both CC pins and look for a connection.