THREE-WIRE (SPI) SERIAL CONTROL

CONTROL DATA WORD FORMAT

ADR6

0

RegisterAddress

RegisterData

ADR5

ADR4

ADR3

ADR2

ADR1

ADR0

D7

D6

D5

D4

D3

D2

D1

D0

MSB

LSB

REGISTER WRITE OPERATION

MS

MC

MD

X

(1)

'0'

ADR6 ADR5 ADR4 ADR3 ADR2 ADR1 ADR0

D7

D6

D5

D4

D3

D2

D1

D0

X

X

0

ADR6

PCM1789

Table 10. FMT Functionality

FMT

DESCRIPTION

Low

High

16-/20-/24-/32-bit left-justified format

The PCM1789 includes an SPI-compatible serial port that operates asynchronously with the audio serial

interface. The control interface consists of MD/SDA/DEMP, MC/SCL/FMT, and MS/ADR0/RSV. MD is the serial

data input used to program the mode control registers. MC is the serial bit clock that shifts the data into the

control port. MS is the select input used to enable the mode control port.

All single write operations via the serial control port use 16-bit data words. Figure 29 shows the control data word

format. The first bit (fixed at '0') is for write operation. After the first bit are seven other bits, labeled ADR[6:0],

that set the register address for the write operation. ADR6 is determined by the status of the MODE pin. ADR5 is

determined by the state of the ADR5/ADR1/RSV pin. A maximum of four PCM1789s can be connected on the

same bus at any one time. Each PCM1789 responds when receiving its own register address. The eight least

significant bits (LSBs), D[7:0] on MD, contain the data to be written to the register address specified by ADR[6:0].

Figure 29. Control Data Word Format for MD

Figure 30 shows the functional timing diagram for single write operations on the serial control port. MS is held at

a high state until a register is to be written to. To start the register write cycle, MS is set to a low state. 16 clocks

are then provided on MC, corresponding to the 16 bits of the control data word on MD. After the 16th clock cycle

has been completed, MS is set high to latch the data into the indexed mode control register.

In addition to single write operations, the PCM1789 also supports multiple write operations, which can be

performed by sending the N-bytes (where N

≤ 9) of the 8-bit register data that follow after the first 16-bit register

address and register data, while keeping the MC clocks and MS at a low state. Ending a multiple write operation

can be accomplished by setting MS to a high state.

(1) X = don't care.

Figure 30. Register Write Operation

Copyright © 2008, Texas Instruments Incorporated

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