WM9713 datasheet(65/111 Pages) WOLFSON

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Preliminary Technical Data

WM9713L

PTD, March 2004, Rev 2.2

INITIATION OF MEASUREMENTS

The WM9713L 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

74h, bit 9). This bit automatically resets itself when the measurement is completed.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

POLL

Writing “1” initiates a measurement.

(when CTC is not set)

74h

CTC

0: Polling mode

1: Continuous mode (for DMA)

76h

9:8

Continuous mode rate (DEL

1111)

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

01: 120 Hz (every 400 AC-Link frames)

10: 153.75 Hz (every 312 AC-Link frames)

11: 187.5Hz (every 256 AC-Link frames)

Continuous mode “fast 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)

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)

78h

PDPOL

Sets polarity of PENDOWN flag:

0: non-inverted

1: inverted

Table 47 Touchpanel Digitiser Control (Initiation of Measurements)

In continuous mode (CTC = 1), the WM9713L autonomously initiates measurements (or sets of

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.

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