SWRU543B January 2019 – June 2025 CC3230S , CC3230SF , CC3235MODS , CC3235MODSF , CC3235S , CC3235SF
Figure 7-4 shows the format that data transfers follow. After the START condition, a slave address is transmitted. This address is 7 bits long followed by an eighth bit, which is a data direction bit (R/S bit in the I2CMSA register). If the R/S bit is clear, the bit indicates a transmit operation (send), and if it is set, the bit indicates a request for data (receive). A data transfer is always terminated by a STOP condition generated by the master. However, a master can initiate communications with another device on the bus by generating a repeated START condition and addressing another slave without first generating a STOP condition. Various combinations of receive and transmit formats are then possible within a single transfer.
The first 7 bits of the first byte make up the slave address (see Figure 7-5). The eighth bit determines the direction of the message. A 0 in the R/S position of the first byte indicates that the master transmits (sends) data to the selected slave, and a 1 in this position indicates that the master receives data from the slave.