GND

V

DD

PenTouch

X+

Y+

Y

-

HighwhentheX+orY+

driverison,orwhenany

sensorconnection/short-

circuittestsareactivated.

GND

ON

Sense

Viasgotosystemanaloggroundplane.

GND

Highwhen

theX+orY+

driverison.

Control

Logic

R

IRQ

VDD/REF

PENIRQ

Connectto

AnalogSupply

TSC2017

www.ti.com

SBAS472 – DECEMBER 2009

Touch Detect

The PENIRQ can be used as an interrupt to the host. RIRQ is an internal pull-up resistor with a programmable

value of either 50k

Ω (default) or 90kΩ. Write command '1011' (setup command) followed by data '0001' sets the

pull-up to 90k

Ω. NOTE: The first three bits must be '0's and the select bit is the last bit. To change the pull-up

back to 50k

Ω, issue write command '1011' followed by data '0000'.

An example for the Y-position measurement is detailed in Figure 27. The PENIRQ output is pulled high by an

internal pull-up. While in power-down mode with PD0 = 0, the Y– driver is on and connected to GND, and the

PENIRQ output is connected to the X+ input. When the panel is touched, the X+ input is pulled to ground

through the touch screen, and the PENIRQ output goes low because of the current path through the panel to

GND, initiating an interrupt to the processor. During the measurement cycle for X-, Y-, and Z-position, the X+

input is disconnected from the PENIRQ pull-down transistor to eliminate any pull-up resistor leakage current from

flowing through the touch screen, thus causing no errors.

In addition to the measurement cycles for X-, Y-, and Z-position, commands that activate the X-drivers, Y-drivers,

and Y+ and X-drivers without performing a measurement also disconnect the X+ input from the PENIRQ

pull-down transistor, and disable the pen-interrupt output function, regardless of the value of the PD0 bit. Under

these conditions, the PENIRQ output is forced low. Furthermore, if the last command byte written to the

TSC2017 contains PD0 = 1, the pen-interrupt output function is disabled and cannot detect when the panel is

touched. In order to re-enable the pen-interrupt output function under these circumstances, a command byte

must be written to the TSC2017 with PD0 = 0.

When the bus master sends the address byte with the R/W bit = 0, and the TSC2017 sends an acknowledge, the

pen-interrupt function is disabled. If the command that follows the address byte contains PD0 = 0, then the

pen-interrupt function is enabled at the end of a conversion. This action is approximately 100

μs (12-bit mode) or

50

μs (8-bit mode) after the TSC2017 receives a STOP/START condition, following the receipt of a command

byte (see Figure 31 and Figure 30 for further details about when the conversion cycle begins).

In both cases previously listed, it is recommended that whenever the host writes to the TSC2017, the master

processor masks the interrupt associated to PENIRQ. This masking prevents false triggering of interrupts when

the PENIRQ line is disabled in the cases previously listed.

Figure 27. Example of a Pen-Touch Induced Interrupt via the PENIRQ Pin

Copyright © 2009, Texas Instruments Incorporated

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