MC34708 datasheet(83/159 Pages) FREESCALE

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Analog Integrated Circuit Device Data



Freescale Semiconductor

MC34708

Functional Block Description

The touch screen readings can be repeated, as in the following example readout sequence, to reduce the interrupt rate and to

allow for easier noise rejection. The dummy conversion inserted between the different readings allows the references in the

system to be pre-biased for the change in touch screen plate polarity. It will read out as ‘0’.

A touchscreen reading will take precedence over an ADC sequence. If an ADC reading is triggered during a touchscreen event,

the ADC sequence will be overwritten by the Touchscreen data.

The first Touch screen conversion can be delayed from 0 (default) to 600

s by programming the TSDLY1[3:0] bits. The

TSDLY2[3:0] controls the delay between each of the touch screen conversions from 0 to 600

s. TSDLY[2:0] sets the delay after

the last address is converted. TSDLY1, 2, and 3 are set to 0 by default.

To perform a touch screen reading, the processor must do the following:

• Enable the touch screen with TSEN

• Select the touch screen sequence by programming the TSSEL0-TSSEL7 SPI bits.

• Program the TSSTOP[2:0]

• Program the delay between the conversion via the TSDLY1 and TSDLY2 settings.

• Trigger the ADC via the TSSTART SPI bit

• Wait for an interrupt indicating the conversion is done TSDONEI

• And then read out the data in the ADRESULTx registers

Table 75. Touch Screen Action Select

TSSELx[1:0]

Signals Sampled

Dummy to discharge TSREF cap

X plate

Y –plate

Contact

Table 76. TSDLYx[3:0]

TSDLYx[3:0]

Delay in uS

0000

0001

0010

0011

120

0100

160

0101

200

0110

240

0111

280

1000

320

1001

360

1010

400

1011

440

1100

480

1101

520

1110

560

1111

600

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