WM8948ECSSLASHR datasheet(104/189 Pages) WOLFSON

104 / 189 page

WM8948

Production Data

PD, May 2011, Rev 4.1

104

SELECTION OF CONTROL INTERFACE MODE

The WM8948 Control Interface can be configured for I2C mode or SPI modes using the

CIFMODE/GPIO3 pin at power-up. The mode selection is as described in Table 67.

CIFMODE/GPIO3

INTERFACE FORMAT

Low

2 wire

High

3- or 4- wire

Table 66 Control Interface Mode Selection

After the Control Interface Mode has been configured, the MODE_GPIO register bit should be set in

order to latch the selection and to allow GPIO functions to be supported on the CIFMODE/GPIO3

pin. After the MODE_GPIO register bit has been set, the Control Interface mode selection will remain

latched until a Software Reset or Power On Reset occurs. See “General Purpose Input / Output” for

details.

In 2-wire (I2C) Control Interface mode, Auto-Increment mode may be selected. This enables multiple

write and multiple read operations to be scheduled faster than is possible with single register

operations. The auto-increment option is enabled when the AUTO_INC register bit is set. This bit is

defined in Table 67. Auto-increment is disabled by default.

In SPI modes, 3-wire or 4-wire operation may be selected using the SPI_4WIRE register bit. In 3-wire

mode, register readback is provided using the bi-directional pin SDA. In 4-wire mode, register

readback is provided using SDOUT. The SDOUT pin may be configured as CMOS or as Open Drain

using the SPI_OD bit. In 3-wire mode the SDA pin may be configured as CMOS or as Open Drain

using the SPI_OD bit. If the open drain option is selected (SPI_OD = 1) then an external pull-up

resistor is required on the SDOUT or SDA output pin.

The Control Interface configuration bits are described in Table 67.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R20 (14h)

Control

Interface

SPI_OD

SDOUT pin configuration

(applies to 3-wire and 4-wire mode

only)

0 = SDOUT output is CMOS

1 = SDOUT output is open drain

SPI_4WIRE

SPI control mode select

0 = 3-wire using bidirectional SDA

1 = 4-wire using SDOUT

AUTO_INC

Enables address auto-increment

(applies to 2-wire / I2C mode only)

0 = Disabled

1 = Enabled

Table 67 Control Interface Configuration

2-WIRE (I2C) CONTROL MODE

In 2-wire mode, the WM8948 is a slave device on the control interface; SCLK is a clock input, while

SDA is a bi-directional data pin. To allow arbitration of multiple slaves (and/or multiple masters) on

the same interface, the WM8948 transmits logic 1 by tri-stating the SDA pin, rather than pulling it

high. An external pull-up resistor is required to pull the SDA line high so that the logic 1 can be

recognised by the master.

In order to allow many devices to share a single 2-wire control bus, every device on the bus has a

unique 7-bit device ID (this is not the same as the 15-bit address of each register in the WM8948).

The WM8948 device ID is 34h. The LSB of the device ID is the Read/Write bit; this bit is set to logic

1 for “Read” and logic 0 for “Write”.

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