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LH75400/01/10/11 (Preliminary) User's Guide
23.2 ADC Theory of Operation
The ADC block can perform a sequence of measurements without intervention from the
ARM core. Examples include:
• Determining how the touch-screen biasing switches are configured.
• Ascertaining how much settling time is required before making a measurement.
• Determining which input is muxed into the ADC input and which input is muxed into the
ADC reference.
From 1 to 16 different measurements can be performed in a sequence. The number of
steps in the sequence is stored in the PC Register.
The biasing switch configuration, settling time, and ADC mux settings for each of the 1 to
16 measurements in the sequence are stored in an entry in the control bank. The
measurement sequence can be triggered by either software or a Pen Down Interrupt.
The control bank state machine fetches each entry from the control bank and stores it in
the registers LW and HW for the duration of the measurement. When the measurement is
complete, the control bank state machine:
• Stores the ADC result and the control bank instruction number in the
measurement FIFO.
• Obtains the next configuration from the control bank into LW and HW.
When all steps of the sequence are complete, or at a programmed FIFO watermark level,
the control bank state machine can signal the ARM core to read results from the FIFO.
From the FIFO, a program can read each measurement result and corresponding input
configuration, as represented by the control bank instruction number. If the FIFO is full:
• The control bank state machine continues to take measurements
• The state machine triggers the FIFO overrun condition.
The ADC can be programmed to repeat the measurement sequence indefinitely, or to
pause at the end of a sequence and wait for a new Pen Down Interrupt or software trigger.
If the sequence does not repeat continuously, the IHW and ILWCTRL Register values
determine the bias and ADC mux settings until a new measurement sequence is triggered.
Analog-to-Digital Converter/Brownout Detector
6/25/03
23-7
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