WM9705 datasheet(44/55 Pages) WOLFSON

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WM9705

Production Data

PD Rev 4.0 December 2003

POLLING METHOD

The polling method relies on the controller to instruct every operation, i.e. to send an instruction

requesting every individual conversion specifically. A polled conversion is requested by writing a 1

to POLL bit 15 in register 76h, along with the address of the channel to be converted.

The channel to convert is identified by a 3-bit tag word ADR[2-0] written to the Pen control register

76h. This tag has the same value as the value read back with the conversion result, thus

identifying which channel the result is for, see Table 24.

If ADD[2-0] is set to 0 then no

conversion will take place and POLL will be reset.

If the channel to convert is an X or Y pen channel, then the appropriate screen driver switch

configuration is selected first, the screen allowed to settle for a time (selected by programming the

value into the DELAY register, DEL[3-0] in register 76h) and then the screen sample taken and

the conversion made. Figures A2 and A3 show the switch configurations for X and Y plate

conversions. Once the conversion is complete, the result is written into the results register 7Ah

where it is available for readback.

Figure 21 Control of ADC conversions : Polling Method

CO-ORDINATE METHOD

Setting bit COO in register 76h puts the device into Co-ordinate conversion mode.

Co-ordinate method of conversion instructs a sequence of conversions necessary to perform a

pen co-ordinate determination. Most basically this requires an X and a Y conversion but may also

include a pressure measurement. Writing to the POLL bit with COO bit in register 76h set

initiates a set of co-ordinate conversions, the results of which are returned to the controller as

soon as they are available.

If pressure conversion, or an auxiliary conversion are also required as part of the sequence, this is

instructed by writing the appropriate address into the ADR [2-0] bits of register 76h. (X and Y

addresses do not need to be set in this case, as they are implied by the choice of co-ordinate

method of operation). DEL[3-0] delays are applied as for polled operation to all conversions.

Subsequent POLL operations will then return both X and Y conversion results, plus the auxiliary

or pressure conversion result indicated by the value set in ADR[2-0].

Once a conversion is complete, the result is written into the results register 7Ah where it is

available for readback.

Screen Switch

/ Input Mux

mode

EAPD/BUSY

delay = 2 frames

Single coordinate conversion with ADR = 000 (X and Y only) with delay set to 1 (2 frames)

POLL

SYNC

ADR = 001 - X measurement

ADR = 010 - Y measurement

DELAY

CONVERT

DELAY

CONVERT

ADC MODE

Pen Detect or Off

Write to 0x76 with 0x8810

SDOUT

Pen Detect or Off

delay = 2 frames

PENDATA

X measurement data

Y measurement data

external signals

internal signals

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