TLC320AD56C Datasheet, PDF (21/43 Pages) Texas Instruments – Sigma-Delta Analog Interface Circuit

3 Serial Communications
DOUT, DIN, SCLK, FS, and FC are the serial communication signals. The digital output data from the ADC
is taken from DOUT. The digital input data for the DAC is applied to DIN. The synchronizing clock for the
serial communication data and the frame sync is taken from SCLK. The frame synchronization pulse that
encloses the ADC/DAC data transfer interval is taken from FS. For an audio signal data transmitted from
the ADC or to the DAC, primary serial communication is used. To read or write words that control both the
options and the circuit configurations of the device, secondary communication is used.
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 and read the register values described in Appendix A. A primary transfer
occurs for every conversion period. A secondary transfer occurs only when requested. Two methods exist
for requesting a secondary command. The FC terminal can be used to request a secondary communication
by asserting it, or the least significant bit (LSB) of the DAC data within a primary transfer can request a
secondary communication. The selection of which method is enabled is provided in Control 1 register (bit
D0) as shown in Appendix A.
For all serial communications, the most significant bit (MSB) is transferred first. For a 16-bit ADC word and
a 16-bit DAC word, D15 is the MSB and D0 is the LSB. For a 15-bit DAC data word in the 16-bit primary
communication, D15 is the MSB, D1 is the LSB, and D0 is used for the embedded function control. All digital
data values are in 2s-complement format.
These logic signals are compatible with TTL-voltage levels and CMOS current levels (when V_DD = 5 V dc).
These logic signals are also compatible with a 3-V supply.
3.1 Primary Serial Communication
A primary serial communication transmits and receives conversion signal data. The ADC word length is
always 16 bits. The DAC word length depends on the status of D0 in the Control 1 register. After power up
or reset, the device defaults to a 15-bit mode (not 16-bit mode). The DAC word length is 15 bits and the last
bit of the primary 16-bit serial communication word is a function control bit used to request secondary serial
communications. In 16-bit mode, all 16 bits of the primary communications word are used as data for the
DAC and the hardware terminal FC must be used to request secondary communications.
3–1