WM8940CGEFLSLASHV datasheet(63/91 Pages) WOLFSON

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Production Data

WM8940

PD, Rev 4.3, November 2011

CONTROL INTERFACE

SELECTION OF CONTROL MODE AND 2-WIRE MODE ADDRESS

The control interface can operate as either a 3-wire or 2-wire interface. The MODE pin determines

the 2 or 3 wire mode as shown in Table 53.

The WM8940 is controlled by writing to registers through a serial control interface. A control word

consists of 24 bits. The first 7 bits (B23 to B16) are address bits that select which control register is

accessed. The remaining 16 bits (B15 to B0) are register bits, corresponding to the 16 bits in each

control register.

MODE

INTERFACE FORMAT

Low

2 wire

Hi-Z

3 wire

High

3 wire

Table 53 Control Interface Mode Selection

USE OF MODE AS A GPIO PIN IN 3-WIRE MODE

In 3-wire mode, MODE can be used as a GPIO pin. If MODE is being used as a GPIO output, the

partner device doesn’t have to drive MDE - the pin will be pulled-up internally causing 3-wire mode

will be selected. The GPIO function is enabled by setting the MODE_GPIO register bit. The MODE

pin can then be controlled using the GPIO register bits as described in Table 52.

To use MODE as a GPIO input, MODE must be undriven or driven high at start-up. Specifically

MODE must be high or hi-Z during an initial write to the control interface which sets the MODE_GPIO

MODE pin can be used freely as a GPIO input or output.

Figure 33 Example Usage of MODE Pin to Generate a Clock out in 3-wire Mode

This example shows how the MODE_GPIO register bit interfaces to the MODE pad in the case

there MODE is used as a GPIO output. When MODE_GPIO is set, the internal version of

MODE is overridden to high and the MODE pin output driver is enabled. The pull up, which is

used to default 3-wire mode at start-up, is disabled as a power saving measure. MODE_GPIO

cannot be set in 2-wire m–de – this would prevent correct operation of the control interface.

Internal timing is arranged to ensure that the override is in place before the pull-up is disabled.

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