AR1000 Datasheet, PDF (15/37 Pages) Microchip Technology – Resistive Touch Screen Controller

7.9 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 35pF. 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.
7.10 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.
7.11 Touch Reporting Protocol
Touch coordinates are sent from the controller to the host system in a 5-byte data packet, which contains the X-
axis coordinate, Y-axis coordinate, and a “Pen-Up/Down” touch status.
The range for X-axis and Y-axis coordinates is from 0-4095 (12-bit). The realized resolution is 1024, as this
product currently defines, in a non-calibrated state, bits X1:X0 and Y1:Y0 as zeros.
It is recommended that applications be developed to read the 12-bit coordinates from the packet and use them in
a 12-bit format. This enhances the application robustness, as it will work with either 10 or 12 bits of coordinate
information.
The touch coordinate reporting protocol is shown below.
Byte #
1
2
3
4
5
Bit 7
1
0
0
0
0
Bit 6
R
X6
0
Y6
0
Bit 5
R
X5
0
Y5
0
Bit 4
R
X4
X11
Y4
Y11
Bit 3
R
X3
X10
Y3
Y10
Bit 2
R
X2
X9
Y2
Y9
Bit 1
R
X1
X8
Y1
Y8
Bit 0
P
X0
X7
Y0
Y7
Table 7 : Touch Coordinate Reporting Protocol
where:
P
: 0 Pen-Up, 1 Pen-Down
R
: Reserved
X11-X0 : X-axis coordinate
Y11-Y0 : Y-axis coordinate
© 2009 Microchip Technology, Inc.
DS41393A-Page 11