DSD1796

SLES101A – DECEMBER 2003 – REVISED NOVEMBER 2006

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SERIAL CONTROL INTERFACE

The serial control interface is a 4-wire synchronous serial port, which operates asynchronously with the serial audio

interface and the system clock (SCK). The serial control interface is used to program and read the on-chip mode registers.

The control interface includes MDO (pin 13), MDI (pin 11), MC (pin 12), and MS (pin 10). MDO is the serial data output,

used to read back the values of the mode registers; MDI is the serial data input, used to program the mode registers; MC

is the serial bit clock, used to shift data in and out of the control port; and MS is the mode control enable, used to enable

the internal mode register access.

Register Read/Write Operation

All read/write operations for the serial control port use 16-bit data words. Figure 28 shows the control data word format.

The most significant bit is the read/write (R/W) bit. For write operations, the R/W bit must be set to 0. For read operations,

the R/W bit must be set to 1. There are seven bits, labeled IDX[6:0], that hold the register index (or address) for the read

and write operations. The least significant eight bits, D[7:0], contain the data to be written to, or the data that was read from,

the register specified by IDX[6:0].

Figure 29 shows the functional timing diagram for writing or reading the serial control port. MS is held at a logic 1 state until

a register needs to be written or read. To start the register write or read cycle, MS is set to logic 0. Sixteen clocks are then

provided on MC, corresponding to the 16 bits of the control data word on MDI and readback data on MDO. After the eighth

clock cycle has completed, the data from the indexed-mode control register appears on MDO during the read operation.

After the sixteenth clock cycle has completed, the data is latched into the indexed-mode control register during the write

operation. To write or read subsequent data, MS must be set to 1 once.

MSB

LSB

Register Index (or Address)

Register Data

R/W

IDX6

IDX5

IDX4

IDX3

IDX2

IDX1

IDX0

D7

D6

D4

D5

D3

D2

D1

D0

Figure 28. Control Data Word Format for MDI

High Impedance

When Read Mode is Instructed

A0

D7

D6

D4

D5

D3

D2

D1

D0

D7

D6

D4

D5

D3

D2

D1

D0

R/W

A1

A2

A3

A4

A5

A6

MS

MC

MDI

MDO

NOTE: Bit 15 is used for selection of write or read. Setting R/W = 0 indicates a write, while R/W = 1 indicates a read. Bits 14–8 are used for the register

address. Bits 7–0 are used for register data.

Figure 29. Serial Control Format