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LH75400/01/10/11 (Preliminary) User's Guide
23.3.2.7 Sequence Start Mode Issues
Setting the SSM bits to 10 does not generate a Pen IRQ. However, when the Idle Mode is
configured to generate a Pen IRQ for a 4-wire Touch Screen, the Pen IRQ detect signal
goes LOW on Pen Down. To address this issue, configure the Idle Mode for a Pen IRQ
using the Pen-measurement sequence:
1.
Idle Step: Configure for Pen Down detect.
2.
Connect the AN0 pin to AVDD_ADC to discharge any charge stored in debounce
capacitors.
3.
Configure for pen down detect.
4.
Measure X.
5.
Measure Y.
6.
Connect the AN0 pin to AVDD_ADC to discharge any charge stored in debounce
capacitors.
7.
Configure for Pen Down detect.
a. Set the NOC bits (bits [3:0]) of the PC Register to 1 (two measurements) and set
b.
c.
If the pen is not still down, set the SSM field back to pen-triggered measurements. Other-
wise, start a Pen Down debounce timer, change the PCR NOC field to 5 (all six measure-
ment steps), and change the End-of-Sequence Interrupt handler to be one that handles all
six measurements.
the SSM bits of this register for pen-triggered measurements.
Set up a Pen Interrupt handler that changes the SSM field to SSB-triggered mea-
surements. This prevents Pen Down from retriggering additional measurements.
Set up an End-of-Sequence Interrupt handler that reads out and discards the
results from step 2, then reads the results from step 3 to see whether the voltage
read indicates that the pen is still down.
Analog-to-Digital Converter/Brownout Detector
6/25/03
23-17
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