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WAN-0143

Wolfson Microelectronics plc
Part Number WAN-0143
Manufacturer Wolfson Microelectronics plc
Description ADA and MASK Timing on WM9712
Published Apr 17, 2005
Detailed Description w INTRODUCTION WAN-0143 ADA and MASK Timing on WM9712 This applications note has been created to detail the timing of...
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WAN-0143
WAN-0143

Overview
w INTRODUCTION WAN-0143 ADA and MASK Timing on WM9712 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 MASK ADA GPIO REGISTER 56H BIT 4 SETTING (GPIO FUNCTION SELECT) 1 1 0 REGISTER 4CH BIT 4 SETTING (PIN DEFINED AS INPUT OR OUTPUT) 1 (Input) 0 (Output) 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] 00 01 10 EFFECT OF SIGNAL ON MASK PIN MASK has no effect on conversions GPIO input disabled (default) Static; ‘hi’ on MASK pin stops conversions, ‘lo’ has no effect.
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.
Synchronous mode; conversions ...


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