SAM9RL Touch Screen ADC Controller

ARM-Based Products Group 2 Resistive touch panel technology is the most common, due to its simplicity and low cost characteristics. It can be found in PDAs, Mini Notebook, Phone, Medical Equipment, Office Automation, Consumer Products, POS, information servers, … Analogue resistive technology can be separated into 4-wire, 5-wire, 6- wire, 7-wire, and 8-wire according to screen size. The most popular are 4-wire and 5-wire systems The SAM9RL64 TSADC is dedicated to 4-wire resistive touch panel ( >15’’ diagonal can be found) Introduction to Resistive Touch panel

ARM-Based Products Group 3  Based on a 10-Bit SAR ADC  ADVREF range from 2.6V to VDDANA.  Up to 6 analog lines with 4 touch screen channels (can be used as normal ADC)  4 power switches measuring both axis (X,Y) on resistive touch screen panel  Pen Detect and Pen Loss interrupt  Trigger Mode: External Trigger, Continuous, Periodic, Pen detect Touch Screen ADC Controller: Block Diagram 6

ARM-Based Products Group 4 Resistive Touch screen Principle Polyester Film Upper Resistive Circuit Layer Conductive ITO (Transparent Metal Coating) Lower Resistive Circuit Layer Insulating Dots Glass - Substrate A press causes the Upper Resistive Circuit Layer to contact the Lower Resistive Circuit Layer, producing a circuit switch from the activated area.

ARM-Based Products Group 5 The 4-Wire Resistive TS Structure Voltage Measurement GND = 0V VDD = 3V VY+ = 1.5V X+ X- Y+Y- Glass VDD GND PEN contact The ratio of this measured voltage to the drive voltage applied is equal to the ratio of the x coordinate to the width of the touch screen. => x = ½ width of touch screen  X Position

ARM-Based Products Group 6  To detect the position of a contact:  Supply voltage is applied between Xp and Xm  Voltage measured on Yp  Supply voltage is applied between Yp and Ym  Voltage measured on Xp  The position is defined by [ (VYp / VDD), (VXp / VDD) ] TSADCC: Position Measurement

ARM-Based Products Group 7 The switches added to control the power supply are resistive: High voltage reference is not VDDANA Low Voltage reference is not GND Compensation of switches loss is necessary : [ X,Y ] [ (VYp – VXm) / (VXp – VXm), (VXp – VYm) / (VYp – VYm) ] TSADCC: Position Measurement

ARM-Based Products Group 8  At each trigger, the touch screen inputs are converted with the switches accordingly set and the results are processed and stored in the corresponding data registers (6 ADC conversions):  (VXp – VXm)  TSADCC_CDR0 register  (VYp – VXm)  TSADCC_CDR1 register  (VYp – VYm)  TSADCC_CDR2 register  (VXp – VYm)  TSADCC_CDR3 register  The vertical position X  X = (VYp – VXm) / (VXp – VXm) = CDR1 / CDR0  The horizontal position Y  Y = (VXp – VYm) / (VYp – VYm) = CDR3 / CDR2 TSADCC: Position Measurement

ARM-Based Products Group 9  No conversion necessary to detect a pen contact  No contact  No current flow  When contact occurs, a current is flowing in the touch screen and a schmitt trigger detects the voltage in the resistor. TSADCC: Pen Detection

ARM-Based Products Group 10 TSADCC: Conversion Events in Pen Detect Mode time Release NOCNT Release NOCNT Wrong value Startup Time SHTIMTS Debounce Time Conversion time Priority to Conversion vs NOCNT => Last conversion may be corrupted Press PENCNTEOC x6 EOC end of conversion

ARM-Based Products Group 11 TSADCC: Conversion Events in Periodic Trigger Mode Trigger period EOC Release EOC time NOCNT Press PENCNT x6 Trigger period Startup Time SHTIMTS Debounce Time Conversion time EOC end of conversion

ARM-Based Products Group 12 Trigger period EOC Press PENCNTEOC x6 Release time NOCNT can not be detected To get the NOCNT status: Ttrigger > 6 x (SHTIMTS + Tconv) + Tdebounce EOC x6 TSADCC: Conversion Events in Periodic Trigger Mode Trigger period Startup Time SHTIMTS Debounce Time Conversion time EOC end of conversion

ARM-Based Products Group 13 TSADCC: Touch Screen Connection X+ X- Y+Y- Glass SAM9RL AD0 (Right) AD1 (Left) AD2 (Top) AD3 (Bottom)

SAM9RL Touch Screen ADC Controller

ARM-Based Products Group 15 6 ADC Conversions requirement 1. If SLEEP is set, wake up the ADC cell and wait for the Startup Time. 2. Close the switches on the inputs XP and XM during the Sample and Hold Time. 3. Convert Channel XM and store the result in TSADCC_CDR1. 4. Close the switches on the inputs XP and XM during the Sample and Hold Time. 5. Convert Channel XP, subtract TSADCC_CDR1 from the result and store the subtraction result in both TSADCC_CDR0 and TSADCC_LCDR. 6. Close the switches on the inputs XP and XM during the Sample and Hold Time. 7. Convert Channel YP, subtract TSADCC_CDR1 from the result and store the subtraction result in both TSADCC_CDR1 and TSADCC_LCDR. 8. Close the switches on the inputs YP and YM during the Sample and Hold Time. 9. Convert Channel YM and store the result in TSADCC_CDR Close the switches on the inputs YP and YM during the Sample and Hold Time. 11. Convert Channel YP, subtract TSADCC_CDR3 from the result and store the subtraction result in both TSADCC_CDR2 and TSADCC_LCDR. 12. Close the switches on the inputs YP and YM during the Sample and Hold Time. 13. Convert Channel XP, subtract TSADCC_CDR3 from the result and store the subtraction result in both TSADCC_CDR3 and TSADCC_LCDR. 14. If Channel 4 to Channel 5 are enabled, convert the Channels and store result in the corresponding TSADCC_CDRx and TSADCC_LCDR. 15. If SLEEP is set, sleep down the ADC cell.