TLC320AD55 Datasheet, PDF (19/41 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 signal (audio) 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 sets up and reads 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. Terminal FC can request a secondary communication when it is
asserted, or the 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 0) as shown in Appendix A.
For all serial communications, the most significant bit is transferred first. For a 16-bit ADC word and a 16-bit
DAC word, D15 is the most significant bit and D0 is the least significant bit. For a 15-bit DAC data word in
the 16-bit primary communication, D15 is the most significant bit, D1 is the least significant bit, 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.
3.1 Primary Serial Communication
Primary serial communication is used both to transmit and receive 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 the 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 the 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