Datasheet

Analog Integrated Circuit Device Data
Freescale Semiconductor 82
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
00 Dummy to discharge TSREF cap
01 X plate
10 Y –plate
11 Contact
Table 76. TSDLYx[3:0]
TSDLYx[3:0] Delay in uS
0000 0
0001 40
0010 80
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