Figure 9-1 shows a serial interface between the DACx311 and a typical 8051-type microcontroller. The setup for the interface is as follows: TXD of the 8051 drives SCLK of the DACx311, while RXD drives the serial data line of the device. The SYNC signal is derived from a bit programmable pin on the port. In this case, port line P3.3 is used. When data are to be transmitted to the DACx311, P3.3 is taken low. The 8051 transmits data only in 8-bit bytes; thus, only eight falling clock edges occur in the transmit cycle. To load data to the DAC, P3.3 remains low after the first eight bits are transmitted, and a second write cycle is initiated to transmit the second byte of data. P3.3 is taken high following the completion of this cycle. The 8051 outputs the serial data in a format that has the LSB first. The DACx311 requires data with the MSB as the first bit received. Therefore, the 8051 transmit routine must take this requirement into account, and mirror the data as needed.

Figure 9-1 DACx311 to 80C51/80l51 Interfaces