4–1
4 Serial Communications
DT_DOUT, DT_DIN, DT_SCLK, and DT_FS, are the serial communication signals for the serial port. The digital
output data from the ADC is taken from DT_DOUT. The digital input data for the DAC is applied to DT_DIN. The
synchronization clock for the serial communication data and the frame-sync is taken from DT_SCLK. The frame-sync
pulse, which signals the beginning of the ADC and DAC data transfer interval, is taken from DT_FS.
For signal data transmitted from the ADC or to the DAC, a primary serial communication is used. A secondary
communication is used to read or write words to the control registers, which control both the options and the circuit
configurations of the device.
The purpose of the primary and secondary communications is to allow conversion data and control data to be
transferred across the same serial port. A primary transfer is always dedicated to conversion data. A secondary
transfer is used to set up or read the control register values described in Appendix A Programmable Register Set.
A primary transfer occurs for every conversion period. A secondary transfer occurs only when requested. Secondary
serial communication is requested by software (D0 of the primary data input to DT_DIN). Control registers 1 and 2
can only be read/write from/to the serial port.
4.1
Primary Serial Communication
Primary serial communication is used to both transmit and receive conversion signal data. The DAC word length is
15 bits and the last bit of the primary 16-bit serial communication word is a control bit used to request secondary serial
communication. For all serial communications, the most significant bit is transferred first. For the 16-bit ADC word,
D15 is the most significant bit and D0 is the least significant bit. For the 15-bit DAC data word in a primary
communication, D15 is the most significant bit, D1 is the least significant bit, and D0 is used for the secondary
communication request control. All digital data values are in 2s-complement data format. Refer to Figure 4–1.
D15–D1
D0
DT_DIN
D15–D0
A/D Data
DT_DOUT
Secondary
Communication Request
D/A Data
Figure 4–1. Primary Communication DIN and DOUT Data Format