Advanced Information

WM8722

WOLFSON MICROELECTRONICS LTD

AI Rev 1.5 May 2000

13

LATCH STATE

Address

1

1000001

0

1000000

To control the WM8722 on the bus, the master must initiate a data transfer by establishing a start

condition, defined by a high-to-low transition on MD whilst MC remains high. This indicates that an

address and data transfer will follow. All peripherals respond to the start condition and shift the next

eight bits (7-bit address + R/W bit). The transfer is MSB first. The peripheral that recognises the

transmitted address responds by pulling the data line low during the ninth clock pulse (acknowledge

bit). All other devices withdraw from the bus and maintain an idle condition once the appropriate

peripheral has been recognised. The idle condition is where the device monitors the MD and MC

lines waiting for a start condition and the correct transmitted address. The R/W bit determines the

direction of data transfer. The WM8722 is a write only device and only responds to the R/W bit

indicating a write.

The WM8722 acts as a standard slave device on the bus. The data on the MD is clocked in by MC.

The first 6 bits (which must be 100000) are clocked into the WM8722 followed by a programmable

address bit to select one of the two available addresses. The eighth bit of the address byte is the

R/W bit. The WM8722 checks this bit and responds if it is a write. If the correct address is sent by

the master, the WM8722 acknowledges the bus master (ACK) and pulls the bus low. The next byte is

the register address. Each subsequent byte of data is separated by an acknowledge bit.

A stop condition is defined when there is a low-to-high transition on MD when MC is high.

If a stop or start condition is detected out of sequence at any point in the data transfer, the device

jumps to the idle condition.

SERIAL CONTROL OPERATION

Control of the various modes of operation is software control over the 2 or 3-wire serial interface. The

following functions may be controlled via the serial control interface:

FUNCTION

OPTIONS

SOFTWARE CONTROL

DEFAULT VALUE

Input audio data format

Normal format

I

Normal format (0)

Input Word Length

16

20

24

16 bit (0)

De-emphasis selection

On

Off

Off (0)

Operation enable (OPE)

(power down)

Enable

disable

Enabled (0)

Analogue output mode

L, R, mono, Mute

Stereo (1001)

Mute

On (Muted)

Off (Un-muted)

Off (0)

Input LRCIN polarity

Lch/Rch = Hi/Lo

Lch/Rch = Lo/Hi

Lch/Rch = Hi/Lo (0)

Master Volume Control

Lch, Rch individually

Lch, Rch both

0dB (1111001)

Lch, Rch individually (0)