Transcript SAM7 Hardware Considerations

SAM9RL Touch Screen ADC Controller
Introduction to Resistive Touch panel
 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, 6wire, 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)
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Touch Screen ADC Controller: Block Diagram
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 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
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Resistive Touch screen Principle
Conductive ITO
Polyester Film
(Transparent Metal Coating)
Upper Resistive Circuit Layer
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.
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The 4-Wire Resistive TS Structure
PEN contact
Voltage
 X Position
Measurement
VDD
X+
VDD = 3V
X-
GND
VY+ = 1.5V
Y-
Y+
Glass
GND = 0V
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
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TSADCC: Position Measurement
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To detect the position of a contact:
1.
Supply voltage is applied between Xp and Xm
2.
Voltage measured on Yp
3.
Supply voltage is applied between Yp and Ym
4.
Voltage measured on Xp
The position is defined by [ (VYp / VDD) , (VXp / VDD) ]
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TSADCC: Position Measurement
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) ]
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TSADCC: Position Measurement
 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
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TSADCC: Pen Detection
 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.
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TSADCC: Conversion Events in Pen Detect Mode
PENCNT
EOC
NOCNT
NOCNT
time
x6
Press
Wrong value
Release
Startup Time
Debounce Time
SHTIMTS
Conversion time
Release
EOC end of conversion
Priority to Conversion vs NOCNT
=> Last conversion may be corrupted
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TSADCC: Conversion Events in Periodic Trigger Mode
Trigger period
PENCNT
Trigger period
EOC
EOC
NOCNT
time
x6
x6
Release
Press
Startup Time
Debounce Time
SHTIMTS
Conversion time
EOC end of conversion
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TSADCC: Conversion Events in Periodic Trigger Mode
Trigger period
Trigger period
Trigger period
EOC
EOC
PENCNT EOC
NOCNT can not
be detected
time
x6
x6
x6
Release
Press
Startup Time
Debounce Time
SHTIMTS
Conversion time
EOC end of conversion
To get the NOCNT status:
Ttrigger > 6 x (SHTIMTS + Tconv) + Tdebounce
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TSADCC: Touch Screen Connection
SAM9RL
X+
AD0 (Right)
X-
AD1 (Left)
AD2 (Top)
AD3 (Bottom)
Y-
Y+
Glass
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SAM9RL Touch Screen ADC Controller
6 ADC Conversions requirement
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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_CDR3.
10. 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.
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