WM9705 datasheet(50/55 Pages) WOLFSON

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WM9705

Production Data

PD Rev 4.4 August 2006

PDD[3-0]

PEN DETECT

THRESHOLD

PDD[3-0]

PEN DETECT

THRESHOLD

0000

Use zero power comp.

1000

8Vmid/15

0001

Vmid/15

1001

9Vmid/15

0010

2Vmid/15

1010

10Vmid/15

0011

3Vmid/15

1011

11Vmid/15

0100

4Vmid/15

1100

12Vmid/15

0101

5Vmid/15

1101

13Vmid/15

0110

6Vmid/15

1110

14Vmid/15

0111

7Vmid/15

1111

Vmid

Table 29 Pen Detect Comparator Threshold

Figure 25 shows the pen detection function schematically.

Y+

X+

X-

Rpen

Xswn

Yswp

Rpusw

Rpu

Pen detect

threshold

setting DAC

4 bit

mux

sel

PENDET

zero power comparator

precision comparator

Y-

Figure 25 Pen Detection Configuration

STANDBY OPERATION AND WAKE-UP

WM9705 allows for complete zero power standby operation, and wake-up-on-pen-down.

That is, all features of the device can be put into zero quiescent current standby, including the

digital interfaces, and the device will wait consuming near zero power until it is re-awoken via pen

down event or via activity on the AC link.

The AC link interface specification allows for standby operation, with all clocks stopped and the

oscillator powered down, (all PR bits set). From this state, either the controller or the Codec can

re-awaken the AC link. This feature is used by WM9705 to allow the standby operation, and wake

on pen down function.

Once in standby, (all PR bits set and Pen digitiser power down control bits PRP{1:0] in reg 78h

set to), the device awaits detection of pen down. Once this occurs, PRP[1] is set to active (1) and

the pen digitiser wakes up, toggles the PENDET pin, and wakes the AC link by toggling the

SDATAIN line. It is then up to the link controller how to respond. It will then toggle the SYNC

signal, which causes the codec to wake up the AC link by re-setting PR4, waking the oscillator

and starting to send BITCLKs. If RPR is set then pen down will also automatically reset PR4 and

wake up the codec.

If the PRP[1:0] is set to 10, then the device is NOT woken on pen down detect, but the PENDET

flag is toggled on pin 46 when the pen is detected as ‘down’. The controller may then wake up the

AC link and hence set PRP[1] bit if it so wishes.

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