SNLS543 August 2018 DS90UH949A-Q1
The DS90UH949A-Q1 contains two downstream ports, therefore some registers must be duplicated to allow control and monitoring of the two ports. To facilitate this, a TX_PORT_SEL register controls access to the two sets of registers. Registers that are shared between ports (not duplicated) will be available independent of the settings in the TX_PORT_SEL register.
Setting the TX_PORT0_SEL or TX_PORT1_SEL bit will allow a read of the register for the selected port. If both bits are set, port1 registers will be returned. Writes will occur to ports for which the select bit is set, allowing simultaneous writes to both ports if both select bits are set.
Setting the PORT1_I2C_EN bit will enable a second I2C slave address, allowing access to the second port registers through the second I2C address. If this bit is set, the TX_PORT0_SEL and TX_PORT1_SEL bits will be ignored.