WM9713 datasheet(72/111 Pages) WOLFSON

72 / 111 page

WM9713L

Preliminary Technical Data

PTD, March 2004, Rev 2.2

MASK INPUT CONTROL

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 / pin 3) to delay or synchronise the sampling of any input to the ADC.

The effect of the MASK signal depends on the the MSK bits of register 78h (bits [7:6]), as described

below.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

78h

7:6

MSK

MASK input control (see Table 55)

Table 54 MASK Input Control

MSK[1-0]

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 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 55 Controlling the MASK Feature

Note that pin 47 / pin 3 can also be used as a GPIO(see “GPIO and Interrupt Control” section), or to

output the ADA signal (see below).

THE ADA SIGNAL

Whenever data becomes available from the touchpanel ADC, the internal ADA (ADC Data Available)

signal goes high and remains high until the data has been read from register 7Ah (if SLEN = 0) or

until it has been sent out on an AC-Link slot (if SLEN = 1).

ADA goes high either-

•

After every touchpannel ADC conversion (in normal mode, COO=0)

•

After every set of 3 conversions (co-ordinate mode, COO=1)

ADA can be used to generate an interrupt, if the AW bit (register 52h, bit 12) is set (see “GPIO and

interrupt control” section)

It is also possible to output the ADA signal on pin 47 / pin 3, if this pin is not used as a GPIO. The

GE4/6 bit must be set to ‘0’ to achieve this (see “GPIO and interrupt control” section).

Alternatively, ADA can be read from bit 12 in register 54h.

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