The DS90UB954-Q1 implements an I2C-compatible target capable of operation compliant to the Standard, Fast, and Fast-plus modes of operation allowing I2C operation at up to 1-MHz clock frequencies. Local I2C transactions to access DS90UB954-Q1 registers can be conducted 2 ms after power supplies are stable and PDB is brought high. For accesses to local registers, the I2C Target operates without stretching the clock. The primary I2C target address is set through the IDx pin. The primary I2C target address is stored in the I2C Device ID register at address 0x0. In addition to the primary I2C target address, the DS90UB954-Q1 may be programmed to respond to up to two other I2C addresses. The two RX Port ID addresses provide direct access to the Receive Port registers without needing to set the paging controls normally required to access the port registers.