Datasheet AR 1021, AR 1011 Datasheet
AR1000 Series Resistive
Touch Screen Controller
Data Sheet
2009-2012 Microchip Technology Inc. Preliminary DS41393B
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QUALITY MANAGEMENT S
DS41393B-page 2 Preliminary 2009-2012 Microchip Technology Inc.
ISBN: 9781620761366
Microchip received ISO/TS-16949:2009 certification for its worldwide
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®
MCUs and dsPIC® DSCs, KEELOQ
®
code hopping
AR1000 SERIES RESISTIVE TOUCH
SCREEN CONTROLLER
AR1000 Series Resistive Touch Screen Controller
Special Features:
• RoHS Compliant
• Power-Saving Sleep mode
• Industrial Temperature Range
• Built-in Drift Compensation Algorithm
• 128 Bytes of User EEPROM
Power Requirements:
• Operating Voltage: 2.5-5.0V ±5%
• Standby Current:
- 5V: 85 uA, typical; 125 uA (maximum)
- 2.5V: 40 uA, typical; 60 uA (maximum)
• Operating “No touch” Current:
- 3.0 mA (typical)
• Operating “Touch” Current:
- 17 mA, typical, with a touch sensor having
200 layers.
- Actual current is dependent on the touch
sensor used
• AR1011/AR1021 Brown-Out Detection (BOR) set
to 2.2V.
Touch Modes:
• Off, Stream, Down, Up and more.
Touch Sensor Support:
• 4-Wire, 5-Wire and 8-Wire Analog Resistive
• Lead-to-Lead Resistance: 50-2,000typical)
• Layer-to-Layer Capacitance: 0-0.5 uF
• Touch Sensor Time Constant: 500 us (maximum)
Touch Resolution:
• 10-bit Resolution (maximum)
Touch Coordinate Report Rate:
• 140 Reports Per Second (typical) with a Touch
Sensor of 0.02 uF with 200 Layers
• Actual Report Rate is dependent on the Touch
Sensor used.
Communications:
• SPI, Slave mode, p/n AR1021
2CTM
•I
• UART, 9600 Baud Rate, p/n AR1011
, Slave mode, p/n, AR1021
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 3
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
Table of Contents
1.0 Device Overview .......................................................................................................................................................................... 5
2.0 Basics of Resistive Sensors......................................................................................................................................................... 7
3.0 Hardware.................................................................................................................................................................................... 11
2
C Communications .................................................................................................................................................................. 17
4.0 I
5.0 SPI Communications.................................................................................................................................................................. 21
6.0 UART Communications.............................................................................................................................................................. 25
7.0 Touch Reporting Protocol........................................................................................................................................................... 27
8.0 Configuration Registers.............................................................................................................................................................. 29
9.0 Commands ................................................................................................................................................................................. 35
10.0 Application Notes ....................................................................................................................................................................... 45
11.0 Electrical Specifications.............................................................................................................................................................. 51
12.0 Packaging Information................................................................................................................................................................ 53
Appendix A: Revision History............................................................................................................................................................... 63
Appendix B: Device Differences........................................................................................................................................................... 64
Index .................................................................................................................................................................................................... 65
The Microchip Web Site....................................................................................................................................................................... 67
Customer Change Notification Service ................................................................................................................................................ 67
Customer Support ................................................................................................................................................................................ 67
Reader Response ................................................................................................................................................................................ 68
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DS41393B-page 4 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
20
19
18
17
16
15
14
13
12
11
V
SS
XX+
5WSX-
YY+
SX+
SDI/SDA/RX
NC
SCK/SCL/TX
1
2
3
4
5
6
7
8
9
10
V
DD
M1
SYM2
WAKE
SIQ
SY+
SS
SDO
NC
AR1000 Series (SSOP, SOIC)
20
19
18
17
16
15
14
13
12
11
X+
5WSX-
YY+
SX+
1
2
3
4
5
6
789
10
SY-
M1
M2
WAKE
SIQ
SY+
SS
VDD
VSS
X-
SDO
NC
SCK/SCL/TX
NC
SDI/SDA/RX
AR1000 Series (QFN)
1.0 DEVICE OVERVIEW
The Microchip mTouchTM AR1000 Series Resistive
Touch Screen Controller is a complete, easy to
integrate, cost-effective and universal touch screen
controller chip.
The AR1000 Series has sophisticated proprietary
touch screen decoding algorithms to process all touch
data, saving the host from the processing overhead.
Providing filtering capabilities beyond that of other
low-cost devices, the AR1000 delivers reliable, validated, and calibrated touch coordinates.
Using the on-board EEPROM, the AR1000 can store
and independently apply the calibration to the touch
coordinates before sending them to the host. This
unique combination of features makes the AR1000 the
most resource-efficient touch screen controller for
system designs, including embedded system
integrations.
FIGURE 1-1: BLOCK DIAGRAM
1.1 Applications
The AR1000 Series is designed for high volume, small
form factor touch solutions with quick time to market
requirements – including, but not limited to:
• Mobile communication devices
• Personal Digital Assistants (PDA)
• Global Positioning Systems (GPS)
• Touch Screen Monitors
•KIOSK
• Media Players
• Portable Instruments
• Point of Sale Terminals
FIGURE 1-2: PIN DIAGRAM
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 5
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
TABLE 1-1: PIN DESCRIPTIONS
Pin
SSOP, SOIC QFN
118 V
2 19 M1 Communication Selection
3 20 SY- Sense Y- (8-wire). Tie to V
4 1 M2 4/8-wire or 5-wire Sensor
5 2 WAKE Touch Wake-up/Touch Detection
6 3 SIQ LED Drive/SPI Interrupt. No
7 4 SY+ Sense Y+ (8-wire). Tie to V
8 5 SS Slave Select (SPI). Tie to V
9 6 SDO SPI Serial Data Output/I
10 7 NC No connection. No connect or tie
11 8 SCK/SCL/TX SPI/I
12 9 NC No connection. No connect or tie
13 10 SDI/SDA/RX I2C™ Serial Data/SPI Serial Data
14 11 SX+ Sense X+ (8-wire). Tie to V
15 12 Y+ Y+ Drive
16 1 3 Y- Y- Drive
17 14 5WSX- 5W Sense (5-wire)/Sense X-
18 15 X+ X+ Drive
19 16 X- X- Drive
20 17 V
Function Description/Comments
DD Supply Voltage
not used.
Selection
connect, if not used.
not used.
not used.
Interrupt. Tie to Vss, if UART.
to VSS or VDD.
2
C™ Serial Clock/UART
Transmit
to VSS or VDD.
Input/UART Receive
not used.
(8-wire). Tie to V
SS Supply Voltage Ground
SS, if
SS, if
SS, if
2
C™
SS, if
SS, if not used.
DS41393B-page 6 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
2.0 BASICS OF RESISTIVE SENSORS
2.1 Terminology
ITO (Indium Tin Oxide) is the resistive coating that
makes up the active area of the touch sensor. ITO is a
transparent semiconductor that is sputtered onto the
touch sensor layers.
Flex or Film or Topsheet
user touches. Flex refers to the fact that the top layer
physically flexes from the pressure of a touch.
Stable or Glass
interfaces against the display.
Spacer Adhesive
the flex and stable layers together around the perimeter
of the sensor.
Spacer Dots
separation between the flex and stable layers. The dots
are typically printed onto the stable layer.
is a frame of adhesive that connects
maintain physical and electrical
is the top sensor layer that a
is the bottom sensor layer that
Bus Bars or Silver Frit electrically connect the ITO on
the flex and stable layers to the sensor’s interface tail.
Bus bars are typically screen printed silver ink. They
are typically much lower in resistivity than the ITO.
is the left and right direction on the touch sensor.
X-Axis
is the top and bottom direction on the touch
Y-Ax is
sensor.
Drive Lines
sensor.
supply a voltage gradient across the
2.2 General
Resistive 4, 5, and 8-wire touch sensors consist of two
facing conductive layers, held in physical separation
from each other. The force of a touch causes the top
layer to deflect and make electrical contact with the
bottom layer.
Touch position measurements are made by applying a
voltage gradient across a layer or axis of the touch
sensor. The touch position voltage for the axis can be
measured using the opposing layer.
A comparison of typical sensor constructions is shown
below in Tabl e 2 -1 .
TABLE 2-1: SENSOR COMPARISON
Sensor Comments
4-Wire Less expensive than 5-wire or 8-wire
Lower power than 5-wire
More linear (without correction) than 5-wire
Touch inaccuracies occur from flex layer damage or resistance changes
5-Wire Maintains touch accuracy with flex layer damage
Inherent nonlinearity often requires touch data correction
Touch inaccuracies occur from resistance changes
8-Wire More expensive than 4-wire
Lower power than 5-wire
More linear (without correction) than 5-wire
Touch inaccuracies occur from flex layer damaged
Maintains touch accuracy with resistance changes
The AR1000 Series Resistive Touch Screen
Controllers will work with any manufacturers of analog
resistive 4, 5 and 8-wire touch screens. The
communications and decoding are included, allowing
the user the quickest simplest method of interfacing
analog resistive touch screens into their applications.
The AR1000 Series was designed with an
understanding of the materials and processes that
make up resistive touch screens. The AR1000 Series
Touch Controller is not only reliable, but can enhance
the reliability and longevity of the resistive touch
screen, due to its advanced filtering algorithms and
wide range of operation.
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 7
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
2.3 4-Wire Sensor
A 4-wire resistive touch sensor consists of a stable and
flex layer, electrically separated by spacer dots. The
layers are assembled perpendicular to each other. The
touch position is determined by first applying a voltage
gradient across the flex layer and using the stable layer
to measure the flex layer’s touch position voltage. The
second step is applying a voltage gradient across the
stable layer and using the flex layer to measure the
stable layer’s touch position voltage.
The measured voltage at any position across a driven
axis is predictable. A touch moving in the direction of
the driven axis will yield a linearly changing voltage. A
touch moving perpendicular to the driven axis will yield
a relatively unchanging voltage (See Figure 2-1).
FIGURE 2-1: 4-WIRE DECODING
DS41393B-page 8 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
2.4 8-Wire Sensor
An 8-wire resistive touch sensor consists of a stable
and flex layer, electrically separated by spacer dots.
The layers are assembled perpendicular to each other.
The touch position is determined by first applying a
voltage gradient across the flex layer and using the
stable layer to measure the flex layer’s touch position
voltage. The second step is applying a voltage gradient
across the stable layer and using the flex layer to
measure the stable layer’s touch position voltage.
The measured voltage at any position across a driven
axis is predictable. A touch moving in the direction of
the driven axis will yield a linearly changing voltage. A
touch moving perpendicular to the driven axis will yield
a relatively unchanging voltage.
FIGURE 2-2: 8-WIRE DECODING
The basic decoding of an 8-wire sensor is similar to a
4-wire. The difference is that an 8-wire sensor has four
additional interconnects used to reference sensor
voltage back to the controller.
A touch system may experience voltage losses due to
resistance changes in the bus bars and connection
between the controller and sensor. The losses can vary
with product use, temperature, and humidity. In a
4-wire sensor, variations in the losses manifest themselves as error or drift in the reported touch location.
The four additional sense lines found on 8-wire sensors
are added to dynamically reference the voltage to correct for this fluctuation during use (See Figure 2-2).
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 9
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
2.5 5-Wire Sensor
A 5-wire resistive touch sensor consists of a flex and
stable layer, electrically separated by spacer dots. The
touch position is determined by first applying a voltage
gradient across the stable layer in the X-axis direction
and using the flex layer to measure the axis touch position voltage. The second step is applying a voltage gradient across the stable layer in the Y-axis direction and
using the flex layer to measure the axis touch position
voltage.
The voltage is not directly applied to the edges of the
active layer, as it is for 4-wire and 8-wire sensors. The
voltage is applied to the corners of a 5-wire sensor.
FIGURE 2-3: 5-Wire Decoding
To measure the X-axis, the left edge of the layer is
driven with 0V (ground), using connections to the upper
left and lower left sensor corners. The right edge is
driven with +5 V
right and lower right sensor corners.
To measure the Y-axis, the top edge of the layer is
driven with 0V (ground), using connections to the upper
left and upper right sensor corners. The bottom edge is
driven with +5 V
and lower right sensor corners.
The measured voltage at any position across a driven
axis is predictable. A touch moving in the direction of
the driven axis will yield a linearly changing voltage. A
touch moving perpendicular to the driven axis will yield
a relatively unchanging voltage (See Figure 2-3).
DC, using connections to the upper
DC, using connections to the lower left
DS41393B-page 10 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
3.0 HARDWARE
3.1 Main Schematic
A main application schematic for the SOIC/SSOP
package pinout is shown in Figure 3-1.
See Figure 1-2 for the QFN package pinout.
FIGURE 3-1: MAIN SCHEMATIC (SOIC/SSOP PACKAGE PINOUT)
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 11
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
3.2 4, 5, 8-Wire Sensor Selection
The desired sensor type of 4/8-wire or 5-wire is
hardware selectable using pin M2.
TABLE 3-1: 4/8-WIRE vs. 5-WIRE
SELECTION
Type M2 pin
4/8-wire V
5-wire VDD
If 4/8-wire has been hardware-selected, then the
choice of 4-wire or 8-wire is software-selectable via the
TouchOptions Configuration register.
When 4/8-wire is hardware-selected, the controller
defaults to 4-wire operation. If 8-wire operation is
desired, then the TouchOptions Configuration register
must be changed.
SS
3.3 4-Wire Touch Sensor Interface
Sensor tail pinouts can vary by manufacturer and part
number. Ensure that both sensor tail pins for one
sensor axis (layer) are connected to the controller’s
X-/X+ pins and the tail pins for the other sensor axis
(layer) are connected to the controller’s Y-/Y+ pins. The
controller’s X-/X+ and Y-/Y+ pin pairs do not need to
connect to a specific sensor axis. The orientation of
controller pins X- and X+ to the two sides of a given
sensor axis is not important. Likewise, the orientation of
controller pins Y- and Y+ to the two sides of the other
sensor axis is not important.
Connections to a 4-wire touch sensor are as follows
(See Figure 3-2).
FIGURE 3-2: 4-WIRE TOUCH SENSOR INTERFACE
Tie unused controller pins 5WSX-, SX+, SY-, and SY+
to V
SS.
See Section 3.8 “ESD Considerations” and
Section 3.9 “Noise Considerations” for important
information regarding the capacitance of the controller
schematic hardware.
DS41393B-page 12 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
3.4 5-Wire Touch Sensor Interface
Sensor tail pinouts can vary by manufacturer and part
number. Ensure sensor tail pins for one pair of
diagonally related sensor corners are connected to the
controller’s X-/X+ pins and the tail pins for the other pair
of diagonally related corners are connected to the
controller’s Y-/Y+ pins.
The controller’s X-/X+ and Y-/Y+ pin pairs do not need
to connect to a specific sensor axis. The orientation of
controller pins X- and X+ to the two selected diagonal
sensor corners is not important.
Likewise, the orientation of controller pins Y- and Y+ to
the other two selected diagonal sensor corners is not
important. The sensor tail pin connected to its top layer
must be connected to the controller’s 5WSX- pin.
Connections to a 5-wire touch sensor are shown in
Figure 3-3 below.
FIGURE 3-3: 5-WIRE TOUCH SENSOR INTERFACE
Tie unused controller pins SX+, SY-, and SY+ to VSS.
See “Section 3.8 “ESD Considerations” and
Section 3.9 “Noise Considerations” for important
information regarding the capacitance of the controller
schematic hardware.
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 13
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
3.5 8-Wire Touch Sensor Interface
Sensor tail pinouts can vary by manufacturer and part
number. Ensure both sensor tail pins for one sensor
axis (layer) are connected to the controller’s X-/X+ pins
and the tail pins for the other sensor axis (layer) are
connected to the controller’s Y-/Y+ pins.
The controller’s X-/X+ and Y-/Y+ pin pairs do not need
to connect to a specific sensor axis. The orientation of
controller pins X- and X+ to the two sides of a given
sensor axis is not important. Likewise, the orientation of
controller pins Y- and Y+ to the two sides of the other
sensor axis is not important.
The 8-wire sensor differs from a 4-wire sensor in that
each edge of an 8-wire sensor has a secondary
connection brought to the sensor’s tail. These
secondary connections are referred to as “sense” lines.
The controller pins associated with the sense line for an
8-wire sensor contain an ‘S’ prefix in their respective
names. For example, the SY- pin is the sense line
connection associated with the main Y- pin connection.
Consult with the sensor manufacturer ’s specification to
determine which member of each edge connected pair
is the special 8-wire “sense” connection. Incorrectly
connecting the sense and excite lines to the controller
will adversely affect performance.
The controller requires that the main and “sense” tail
pin pairs for sensor edges be connected to controller
pin pairs as follows:
• Y- and SY-
• Y+ and SY+
• X- and 5WSX-
• X+ and SX+
Connections to a 8-wire touch sensor are shown in
Figure 3-4 below.
FIGURE 3-4: 8-WIRE TOUCH SENSOR INTERFACE
See Section 3.8 “ESD Considerations” and
Section 3.9 “Noise Considerations” for important
information regarding the capacitance of the controller
schematic hardware.
DS41393B-page 14 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
3.6 Status LED
The LED and associated resistor are optional.
FIGURE 3-5:
The LED serves as a status indicator that the controller
is functioning. It will slow flash when the controller is
running with no touch in progress. It will flicker quickly
(mid-level on) when a touch is in progress.
If the LED is used with SPI communication, then the
LED will be off with no touch and flicker quickly
(mid-level on) when a touch is in progress.
Note: If the SIQ pin is not used, it must be left as
a No Connect and NOT tied to circuit V
SS.
V
DD or
3.7 WAKE Pin
The AR1000’s WAKE pin is described as “Touch
Wake-Up/Touch Detection”. It serves the following
three roles in the controller’s functionality:
• Wake-up from touch
• Touch detection
• Measure sensor capacitance
The application circuit shows a 20 KΩ resistor
connected between the WAKE pin and the X- pin on the
controller chip. The resistor is required for product
operation, based on all three of the above roles.
3.8 ESD Considerations
ESD protection is shown on the 4-wire, 5-wire, and
8-wire interface applications schematics.
The capacitance of alternate ESD diodes may
adversely affect touch performance. A lower
capacitance is better. The PESD5V0S1BA parts shown
in the reference design have a typical capacitance of 35
pF. Test to ensure that selected ESD protection does
not degrade touch performance.
ESD protection is shown in the reference design, but
acceptable protection is dependent on your specific
application. Ensure your ESD solution meets your
design requirements.
3.9 Noise Considerations
Touch sensor filtering capacitors are included in the
reference design.
Warning: Changing the value of the capacitors may
adversely affect performance of the touch system.
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 15
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
NOTES:
DS41393B-page 16 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
4.0 I2CTM COMMUNICATIONS
The AR1021 is an I2C slave device with a 7-bit address
of 0x4D, supporting up to 400 kHz bit rate.
A master (host) device interfaces with the AR1021.
4.1 I2C Hardware Interface
A summary of the hardware interface pins is shown
below in Tab le 4 - 1.
TABLE 4-1: I2C HARDWARE INTERFACE
AR1021 Pin Description
M1 Connect to V
SS to select I
SCL Serial Clock to master I2C
SDA Serial Data to master I
SDO Data ready interrupt output to master
M1 Pin
• The M1 pin must be connected to V
ure the AR1021 for I
2
C communications.
SS to config-
SCL Pin
• The SCL (Serial Clock) pin is electrically
open-drain and requires a pull-up resistor, typically 2.2 K to 10 K, from SCL to V
DD.
• SCL Idle state is high.
SDA Pin
• The SDA (Serial Data) pin is electrically
open-drain and requires a pull-up resistor, typically 2.2K to 10K, from SDA to V
DD.
• SDA Idle state is high.
• Master write data is latched in on SCL rising
edges.
• Master read data is latched out on SCL falling
edges to ensure it is valid during the subsequent
SCL high time.
SDO Pin
• The SDO pin is a driven output interrupt to the
master.
• SDO Idle state is low.
• SDO will be asserted high when the AR1021 has
data ready (touch report or command response)
for the master to read.
2
C™ communications
2
C
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 17
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
4.2 I2C Pin Voltage Level Characteristics
TABLE 4-2: I2C PIN VOLTAGE LEVEL CHARACTERISTICS
Function Pin Input Output
SCL/SCK SCL/SCK/TX V
SDO SDO — V
SDA SDI/SDA/RX VSS ≤ VIL ≤ 0.2*VDD
Note 1: These parameters are characterized but not tested.
2: At 10 mA.
3: At –4 mA.
SS ≤ VIL≤ 0.2*VDD
0.8*VDD ≤ VIH ≤ VDD
0.8*VDD ≤ VIH ≤ VDD
4.3 Addressing
The AR1021’s device ID 7-bit address is: 0x4D
(0b1001101)
TABLE 4-3: I2C DEVICE ID ADDRESS
Device ID Address, 7-bit
A7 A6 A5 A4 A3 A2 A1
1001101
TABLE 4-4: I2C DEVICE WRITE ID
ADDRESS
A7 A6 A5 A4 A3 A2 A1 A0
1 0 011010 0x9A
TABLE 4-5: I2C DEVICE READ ID
A7 A6 A5 A4 A3 A2 A1 A0
1 0 011011 0x9B
4.4 Master Read Bit Timing
Master read is to receive touch reports and command
responses from the AR1021.
• Address bits are latched into the AR1021 on the
rising edges of SCL.
• Data bits are latched out of the AR1021 on the
rising edges of SCL.
• ACK is presented (by AR1021 for address, by
master for data) on the ninth clock.
• The master must monitor the SCL pin prior to
asserting another clock pulse, as the AR1021
may be holding off the master by stretching the
clock.
—
SS ≤ VOL
(1.25*VDD – 2.25V)
Open-drain
(1)
≤ (1.2V – 0.15*VDD)
ADDRESS
(3)
≤ VOH
(1)
≤ VDD
(2)
FIGURE 4-1: I2C MASTER READ BIT TIMING DIAGRAM
Steps
1. SCL and SDA lines are Idle high.
2. Master presents “Start” bit to the AR1021 by
taking SDA high-to-low, followed by taking SCL
high-to-low.
3. Master presents 7-bit Address, followed by a
R/W = 1 (Read mode) bit to the AR1021 on
SDA, at the rising edge of eight master clock
(SCL) cycles.
DS41393B-page 18 Preliminary 2009-2012 Microchip Technology Inc.
4. AR1021 compares the received address to its
device ID. If they match, the AR1021
acknowledges (ACK) the master sent address
by presenting a low on SDA, followed by a
low-high-low on SCL.
5. Master monitors SCL, as the AR1021 may be
“clock stretching”, holding SCL low to indicate
that the master should wait.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
6. Master receives eight data bits (MSb first)
presented on SDA by the AR1021, at eight
sequential master clock (SCL) cycles. The data
is latched out on SCL falling edges to ensure it
is valid during the subsequent SCL high time.
7. If data transfer is not complete, then:
- Master acknowledges (ACK) reception of the
eight data bits by presenting a low on SDA,
followed by a low-high-low on SCL.
- Go to step 5.
8. If data transfer is complete, then:
- Master acknowledges (ACK) reception of the
eight data bits and a completed data transfer
by presenting a high on SDA, followed by a
low-high-low on SCL.
9. Master presents a “Stop” bit to the AR1021 by
taking SCL low-high, followed by taking SDA
low-to-high.
4.5 Master Write Bit Timing
Master write is to send supported commands to the
AR1021.
• Address bits are latched into the AR1021 on the
rising edges of SCL.
• Data bits are latched into the AR1021 on the
rising edges of SCL.
• ACK is presented by AR1021 on the ninth clock.
• The master must monitor the SCL pin prior to
asserting another clock pulse, as the AR1021
may be holding off the master by stretching the
clock.
FIGURE 4-2: I2C MASTER WRITE BIT TIMING DIAGRAM
Steps
1. SCL and SDA lines are Idle high.
2. Master presents “Start” bit to the AR1021 by
taking SDA high-to-low, followed by taking SCL
high-to-low.
3. Master presents 7-bit Address, followed by a
R/W = 0 (Write mode) bit to the AR1021 on
SDA, at the rising edge of eight master clock
(SCL) cycles.
4. AR1021 compares the received address to its
device ID. If they match, the AR1021
acknowledges (ACK) the master sent address
by presenting a low on SDA, followed by a
low-high-low on SCL.
5. Master monitors SCL, as the AR1021 may be
“clock stretching”, holding SCL low to indicate
the master should wait.
6. Master presents eight data bits (MSb first) to the
AR1021 on SDA, at the rising edge of eight master clock (SCL) cycles.
7. AR1021 acknowledges (ACK) receipt of the
eight data bits by presenting a low on SDA, followed by a low-high-low on SCL.
8. If data transfer is not complete, then go to step 5.
9. Master presents a “Stop” bit to the AR1021 by
taking SCL low-high, followed by taking SDA
low-to-high.
4.6 Clock Stretching
The master normally controls the clock line SCL. Clock
stretching is when the slave device holds the SCL line
low, indicating to the master that it is not ready to
continue the communications.
During communications, the AR1021 may hold off the
master by stretching the clock with a low on SCL.
The master must monitor the slave SCL pin to ensure
the AR1021 is not holding it low, prior to asserting
another clock pulse for transmitting or receiving.
4.7 AR1020 Write Conditions
The AR1020 part does not implement clock stretching
on write conditions.
A 50 us delay is needed before the Stop bit, when
clocking a command to the AR1020.
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 19
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
4.8 Touch Report Protocol
Touch coordinates, when available, are provided to the
master by the AR1021 in the following protocol (See
Figure 4-3).
FIGURE 4-3: I2C TOUCH REPORT PROTOCOL
Note that the IRQ signal shown above occurs on the
SDO pin of the AR1021.
4.9 Command Protocol
The master issues supported commands to the
AR1021 in the following protocol.
Below is an example of the ENABLE_TOUCH command
(see Figure 4-4).
FIGURE 4-4: I2C COMMAND PROTOCOL
Note that the IRQ shown above occurs on the SDO pin.
• 0x9A AR1021 Device ID address
• 0x00 Protocol command byte (send 0x00 for
the protocol command register)
• 0x55 Header
• 0x01 Data size
• 0x12 Command
4.10 Sleep State
Pending communications are not maintained through a
sleep/wake cycle.
If the SDO pin is asserted for a pending touch report or
command response, and the AR1021 enters a Sleep
state, prior to the master performing a read on the data,
then the data is lost.
DS41393B-page 20 Preliminary 2009-2012 Microchip Technology Inc.
AR1000 SERIES RESISTIVE TOUCH SCREEN CONTROLLER
5.0 SPI COMMUNICATIONS
SPI operates in Slave mode with an Idle low SCK and
data transmitted on the SCK falling edge.
5.1 SPI Hardware Interface
A summary of the hardware interface pins is shown
below in Tab le 5 - 1.
TABLE 5-1: SPI HARDWARE INTERFACE
AR1021 Pin Description
M1 Connect to V
SDI Serial data sent from master
SCK Serial clock to master
SDO Serial data to master SPI
SIQ
SS
SCK Pin
• The AR1021 controller’s SCL/SCK/TX pin
receives Serial Clock (SCK), controlled by the
host.
• The Idle state of the SCK should be low.
• Data is transmitted on the falling edge of SCK.
SDI Pin
• The AR1021 controller’s SDI/SDA/RX pin reads
Serial Data Input (SDI), sent by the host.
SDO Pin
• The AR1021 controller’s SDO pin presents Serial
Data Output (SDO) to the host.
Interrupt output to master (optional)
Slave Select (optional)
DD to select SPI communications
SIQ Pin
• The AR1021 controller’s SIQ pin provides an
optional interrupt output from the controller to the
host.
• The SIQ pin is asserted high when the controller
has data available (a touch report or a command
response) for the host.
• The SIQ pin is deasserted after the host clocks
out the first byte of the data packet.
Note: The AR1000 Development kit PICkit™
Serial Pin 1 is designated for the SIQ
interrupt pin after the firmware updated is
executed for the PICkit.
SS Pin
• The AR1021 controller’s SS pin provides optional
“slave select” functionality.
SS Pin Level AR1021 Select
VSS
VDD
In the ‘inactive’ state, the controller’s SDO pin presents
a high-impedance in order to prevent bus contention
with another device on the SPI bus.
2009-2012 Microchip Technology Inc. Preliminary DS41393B-page 21
Active
Inactive
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