WM9712CLGEFLSLASHV datasheet(43/78 Pages) WOLFSON

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Production Data

WM9712L

PD, Rev 4.6, November 2011

INITIATION OF MEASUREMENTS

The WM9712L touchpanel interface supports both polling routines and DMA (direct memory access)

to control the flow of data from the touchpanel ADC to the host CPU.

In a polling routine, the CPU starts each measurement individually by writing to the POLL bit (register

76h, bit 15). This bit automatically resets itself when the measurement is completed.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

76h

CTC

0: Polling mode

1: Continuous mode (for DMA)

POLL

Writing “1” initiates a measurement

9:8

Continuous mode rate (DEL ≠ 1111)

00: 93.75 Hz (every 512 AC-Link frames)

01: 187.5 Hz (every 256 AC-Link frames)

10: 375Hz (every 128 AC-Link frames)

11: 750Hz (every 64 AC-Link frames)

Continuous mode rate (DEL = 1111)

00: 8 kHz (every six AC-Link frames)

01: 12 kHz (every four AC-Link frames)

10: 24 kHz (every other AC-Link frame)

11: 48 kHz (every AC-Link frame)

78h

PDEN

0: measure regardless of pen status

1: measure only when pen is down (when

CTC=0 and POLL=1, measurement is

delayed until pen-down; when CTC=1,

measurements are stopped on pen-up)

Table 27 Touchpanel Digitiser Control (Initiation of Measurements)

In continuous mode (CTC = 1), the WM9712L autonomously initiates measurements at the rate set by

CR, and supplies the measured data to the CPU on one of the unused AC’97 time slots. DMA-

enabled CPUs can write the data directly into a FIFO without any intervention by the CPU core. This

reduces CPU loading and speeds up the execution of user programs in handheld systems.

Note that the measurement frequency in continuous mode is also affected by the DEL bits (see

“Touchpanel Settling Time”). The faster rates achieved when DEL = 1111 may be useful when the

ADC is used for auxiliary measurements.

MEASUREMENT TYPES

The ADCSEL control bits determine which type of measurement is performed (see below).

ADDRESS

BIT

LABEL

DEFAULT DESCRIPTION

76h

14:12

ADCSEL

000

Measurement Type (ADC Input Selector)

000: No measurement

001: X co-ordinate measurement

010: Y co-ordinate measurement

011: Pressure measurement

100: COMP1/AUX1 measurement (pin 29)

101: COMP2/AUX2 measurement (pin 30)

110: BMON/AUX3 measurement (pin 31)

111: WIPER/AUX4 measurement (pin 12)

COO

Enable co-ordinate mode

0: Single measurement according to ADCSEL

1: X, then Y, then additional measurement

indicated by ADCSEL

Table 28 Touchpanel Digitiser Control (Measurement Types)

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