Bias-And-Control Network - Sharp LH79524 User Manual

LH79524/LH79525 User's Guide
The Control Bank state machine fetches each entry from the Control Bank and stores it in
the Low Word register (LW) and High Word register (HW) for the duration of the measure-
ment. When the measurement is complete, the Control Bank state machine stores the ADC
result and the Control Bank instruction number in the measurement FIFO, then obtains the
next configuration from the Control Bank and loads it into LW and HW.
When all steps of the sequence are complete, or at a programmed FIFO watermark level,
the Control Bank state machine signals the ARM core to read results from the FIFO.
From the FIFO, software 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 and the state machine
triggers the FIFO Overrun Interrupt.
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, software programs the HW and LW registers with the
contents of the Idle High Word (IHWCTRL) and Idle Low Word (ILWCTRL) register values with
the bias and ADC multiplexer settings until a new measurement sequence is triggered.

2.1.2 Bias-and-Control Network

The bias-and-control network supports 4-, 5-, 7-, and 8-wire touch panels. Multiplexers on
the reference inputs enable connection in both single-ended and ratiometric modes.
• For 4-wire operation, connection is to inputs AN/UL/X+, AN1/UR/X-, AN2/LL/Y+, and
AN3/LR/Y-. Pull-up and pull-down FETs allow X and Y coordinate measurement in addi-
tion to pen-pressure sensing. The Pen Interrupt line is also available via the Interrupt
Masking/Enabling register (see Section 2.2.2.4).
• For 5-wire operation, panel connections are to AN/UL/X+, AN1/UR/X-, AN2/LL/Y+,
AN3/LR/Y-, and AN4/WIPER inputs. The Pen Interrupt line is also available in this mode.
• For 7-wire operation, connections are the same as the 5-wire touch panel with a second
wire added to the Upper Left and Lower Right corners.
• For 8-wire operation, connections are the same as the 4-wire touch panel with a second
wire added to each of the connections. This configuration also requires a single external
MOSFET.
• Details for wiring 4-, 5-, 7, and 8-wire touch panels appear in the application note 'Using
the SHARP ADC with Resistive Touch Screens', available at www.sharpsma.com.
Analog-to-Digital Converter/Brownout Detector
Version 1.0 2-3