WM9712CLGEFLSLASHV datasheet(46/78 Pages) WOLFSON

46 / 78 page

WM9712L

Production Data

PD, Rev 4.6, November 2011

Setting DEL to ‘1111’ reduces the settling time to zero, i.e. measurements begin immediately. This

mode is intended for fast sampling on AUX inputs. It is NOT intended for touchpanel digitisation.

There are several side-effects when DEL is set to ‘1111’:



Co-ordinate mode does not work, i.e. the WM9712L behaves as if COO = 0, even if COO

= 1 (see “Measurement Types”)



If X / Y co-ordinate or touch pressure measurements are selected (ADCSEL = 001, 010 or

011), then the switch matrix is constantly on, and current constantly flows in the

touchpanel. This increases power consumption in the system, and is therefore not

recommended for battery powered systems



In continuous mode (CTC = 1), setting DEL = 1111 increases the sampling rate of the

touchpanel ADC (see “Initiation of Measurements”)

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) to delay or synchronise the sampling of any input to the ADC. The effect

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

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 33 Controlling the MASK Feature

Note that pin 47 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 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, if this pin is not used as a GPIO. The GE4 bit

(register 56h, bit 12) 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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