WM8722

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 1.5 May 2000

12

MODES OF OPERATION

The software control interface may be operated using either a 3-wire (SPI-compatible) or 2-wire MPU

interface. Selection of interface format is achieved by monitoring the state of BUSY pin at power up.

In 3-wire mode, MD is used for the program data, MC is used to clock in the program data and

LATCH is used to latch in the program data. In 2-wire mode, MD is used for serial data and MC is

used for serial clock. In 2-wire mode, the LATCH pin allows the user to select one of two addresses.

SELECTION OF SERIAL CONTROL MODE

The serial control interface may be selected to operate in either 2 or 3-wire modes. This is achieved

by setting the state of the BUSY pin at power-up with a weak, external pull-up or pull-down resistor

(typically 10k). This pin is an input at power up, and its state selects the type of input format. The

value input at power-up is sampled and stored internally. This allows the BUSY pin to be used as an

output when tone generation has been enabled. This stored value is only reset when the device is

powered off.

BUSY PIN (TONE

GENERATION NOT ENABLED)

INTERFACE

FORMAT

03 wire

12 wire

Table 3. Control Interface Mode Selection

3-WIRE (SPI COMPATIBLE) SERIAL CONTROL MODE

The WM8722 can be controlled using a 3-wire serial interface. MD is used for the program data, MC

is used to clock in the program data and LATCH is use to latch in the program data. The 3-wire

interface protocol is shown in Figure 7.

LATCH

MC

MD

B15

B6

B7

B8

B9

B10

B11

B12

B13

B14

B1

B2

B3

B4

B5

B0

Figure 7. 3-Wire Serial Interface

2-WIRE SERIAL CONTROL MODE

The WM8722 supports a 2-wire MPU serial interface. The device operates as a slave device only.

The WM8722 has one of two slave addresses that are selected by setting the state of pin 5,

(LATCH).

MD

MC

ACK

R ADDR

R/W

ACK

ACK

ADDR

DATA B7-0

DATA B15-8

STOP

START

Figure 8. 2-Wire Serial Interface