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SERIAL CONTROL INTERFACE

REGISTER WRITE OPERATION

IDX 5

ID X 6

0

IDX 4

ID X 2

ID X3

ID X 1

ID X0

D 7

D 6

D 5

D4

D 3

D 2

D1

D 0

MSB

Register Index (or Address)

Register Data

LSB

0

D7

D6

D5

D4

D3

D2

0

IDX 6

D1

D0

X

X

X

ID X6

IDX 5

ID X 4

ID X3

ID X 2 ID X1

ID X0

ML

MC

MD

PCM1742

SBAS176A – DECEMBER 2000 – REVISED APRIL 2005

The serial control interface is a 3-wire serial port that operates asynchronously to the serial audio interface. The

serial control interface is used to program the on-chip mode registers. The serial control interface includes

MD (pin 13), MC (pin 14), and ML (pin 15). MD is the serial data input, used to program the mode registers; MC

is the serial bit clock, used to shift data into the control port; and ML is the control-port latch clock.

All write operations for the serial control port use 16-bit data words. Figure 23 shows the control data word

format. The most significant bit must be a 0. Seven bits, labeled IDX[6:0], set the register index (or address) for

the write operation. The least significant eight bits, D[7:0], contain the data to be written to the register specified

by IDX[6:0].

Figure 23. Control Data Word Format for MD

Figure 24 shows the functional timing diagram for writing to the serial control port. ML is held at a logic-1 state

until a register needs to be written. To start the register write cycle, ML is set to logic-0. Sixteen clocks are then

provided on MC, corresponding to the 16 bits of the control data word on MD. After the sixteenth clock cycle has

completed, ML is set to logic-1 to latch the data into the indexed mode control register.

Figure 24. Register Write Operation

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