Cirrus Logic EP93xx - Manual (Page 754)

25-16 DS785UM1
Copyright 2007 Cirrus Logic
Analog Touch Screen Interface
EP93xx User’s Guide
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25.2.6 Polled and Interrupt-Driven Modes
The ADC provides support for synchronous sampling, in both polled mode and interrupt-
driven mode. In either mode, the touch screen scanning state machine should be disabled by
setting bit 15 of the TSSetup register to zero.
The ADC decimation filter conversion value appears in the TSXYResult register. With the
touch screen scanning state machine disabled, bit 31 of this register is the SDR, or
Synchronous Data Ready, bit. This bit is set when a new valid conversion value appears in
this register, and is cleared when this register is read. Hence, in polled mode, the
TSXYResult register may be read repeatedly. If two consecutive reads show the bit clear and
then set, the second read has a new valid value.
Conversion data may also be processed using interrupts from this module. If bit 11 in the
TSSetup2 register (the RINTEN bit) is set, an interrupt occurs whenever the SDR bit in the
TSXYResult register is set. Therefore, an interrupt handler can read the TSXYResult register
whenever a new valid sample appears in the register, which both returns a new conversion
value and clears the interrupt.
25.2.7 Touch Screen Package Dependency
The Touch block uses the following external pins
Table 25-3. External Signal Functions
Signals Function
DAC_VDD Should be connected to ADC_VDD on the board.
ADC_VDD
Touch Screen ADC power, nominal 3.3V. This supply is internally diode connected to the
DAC_VDD supply to provide additional ESD protection.
Should be connected to DAC_VDD on the board.
Xp
Xm
Touch Screen ADC X axis analog bias output.
Yp
Ym
Touch Screen ADC Y axis analog bias output.
sXp
sXm
Touch Screen ADC X axis voltage feedback inputs.
sYp
sYm
Touch Screen ADC Y axis voltage feedback inputs.
ADC_GND Touch Screen ADC ground