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WAN-0143

ADA and MASK Timing on WM9712

WOLFSON MICROELECTRONICS plc

www.wolfsonmicro.com

March 2004, Rev 1.0.

Copyright

2004 Wolfson Microelectronics plc

INTRODUCTION

This applications note has been created to detail the timing of the MASK and ADA (ADC Data

Available) signals on the WM9712 device. This applications note should be used in conjunction with

the latest WM9712 datasheet.

The WM9712 has many additional functions to aid the design of portable applications. Pin 47 of the

device can be configured for either MASK input, ADA output or standard GPIO functionality. The

MASK function can be used to pause and control auxiliary ADC conversions. The ADA function can

be used to indicate when data becomes available from the auxiliary ADC.

The timing associated

with both signals is detailed in the following sections of this document.

WM9712 SETUP

The WM9712 device must be configured to setup the function of pin 47. The three possible setups

are:

•

MASK Input Function

•

ADA Function

•

General GPIO

To set the device into one of the three above modes the following configurations should be used.

PIN 47 MODE

REGISTER 56H BIT 4 SETTING

(GPIO FUNCTION SELECT)

REGISTER 4CH BIT 4 SETTING

(PIN DEFINED AS INPUT OR OUTPUT)

MASK

1

1 (Input)

ADA

1

0 (Output)

GPIO

0

1 or 0 (GPIO can be Input or Output)

Table 1 WM9712 Pin 47 Configuration

MASK FUNCTION

Sources of glitch noise, such as the signals driving an LCD display, may feed through to the

touchscreen plates and affect measurement accuracy. In order to minimise this effect, a signal may

be applied to MASK (pin 47) to delay or synchronise the sampling of any input to the ADC. The effect

of the MASK signal depends on the MSK[1-0] bits of register 78h, as described below.

MSK[1-0]

EFFECT OF SIGNAL ON MASK PIN

00

MASK has no effect on conversions GPIO input disabled (default)

01

Static; ‘hi’ on MASK pin stops conversions, ‘lo’ has no effect.

10

Edge triggered; rising or falling edge on MASK pin delays conversions

by an amount set in the DEL[3-0] register. Conversions are asynchronous to

the MASK signal.

11

Synchronous mode; conversions wait until rising or falling edge on MASK

initiates cycle; screen starts to be driven when the edge arrives, the

conversion sample being taken a period set by DEL[3-0] after the edge.

Table 2 Controlling the MASK Feature