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