One clock pulse is generated by the master device for each data bit transferred. The I2C mode operates with byte data. Data is transferred to MSB first as shown in Figures 1. The first byte after a START condition consists of a 7-bit slave address and the R/W bit. When R/W = 0, the master transmits data to a slave. When R/W = 1, the master receives data from a slave. The ACK bit is sent from the receiver after each byte on the ninth SCL clock.

START and STOP conditions are generated by the master and are shown in Figures 38-3. A START condition is a high-to-low transition on the SDA line while SCL is high. A STOP condition is a low-to-high transition on the SDA line while SCL is high. The bus busy bit, UCBBUSY, is set after a START and cleared after a STOP. Data on SDA must be stable during the high period of SCL (see Figure 38-4). The high and low state of SDA can only change when SCL is low, otherwise, START or STOP conditions are generated.