TSC2004 datasheet(28/62 Pages) TI2

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Touch Screen Scan Function for XYZ or XY

Touch Screen Sensor Connection Tests for X-Axis and Y-Axis

Touch Sensor Short-Circuit Test

TSC2004

SBAS408E – JUNE 2007 – REVISED MARCH 2008

C3-C0 = 0000 or 0001: These scan functions can collaborate with the PSM bit that defines the control mode of

converter functions. If the PSM bit is set to '1', these scan function select commands are recommended to be

issued before a pen touch is detected in order to allow the TSC2004 to initiate and control the scan processes

immediately after the screen is touched. If these functions are not issued before a pen touch is detected, the

TSC2004 waits for the host to write these functions before starting a scan process. If PSM stays as '1' after a

TSC-initiated scan function is complete, the host is not required to write these function select bits again for each

of the following pen touches after the detected touch. In the host-controlled converter function mode (PSM = 0),

the host must send these functions select bits repeatedly for each scan function after a detected pen touch.

Note that the data registers may be updated while a host reading is in progress. Using the sequential read cycle

(see Figure 36) prevents the TSC from updating registers while a host reading is in progress. To ensure that the

XYZ or XY coordinates are correctly read, use the sequential read cycle to read the coordinates after the scan.

Range of resistances of different touch screen panels can be selected by setting the TBM bits in CFR1; see

Table 20. Once the resistance of the sensor panel is selected, two continuity tests are run separately for the

X-axis and Y-axis. The unit under test must pass both connection tests to ensure that a proper connection is

secured.

C3-C0 = 1001: PINTDAV = 0 during this connection test. A '1' shown at end of the test indicates the X-axis

drivers are well-connected to the sensor; otherwise, X-axis drivers are poorly connected. If drivers fail to connect,

then PINTDAV stays low until a stop bit (STS set to '1') is issued.

C3-C0 = 1010: PINTDAV = 0 during this connection test. A '1' shown at end of the test indicates the Y-axis

drivers are well-connected to the sensor; otherwise, Y-axis drivers are poorly connected. If the drivers are fail to

connect, then PINTDAV stays low until a stop bit (STS set to '1') is issued.

If the TBM bits of CFR1 detailed in Table 20 are all set to '1', a short-circuit in the touch sensor can be detected.

C3-C0 = 1011: Reserved.

C3-C0 = 1100: PINTDAV = 0 during this short-circuit test. A '1' shown at end of the test indicates there is no

short-circuit detected (through Y-axis) between the flex and stable layers. If there is a short-circuit detected,

PINTDAV stays low until a stop bit (STS set to '1') is issued.

RM—Resolution select. If RM = 1, the conversion result resolution is 12-bit; otherwise, the resolution is 10-bit.

This bit is the same RM bit shown in CFR0.

SWRST—Software reset input. All register values are set to default value if a '1' is written to this bit. This bit is

automatically set to '0' in order to cancel the software reset and resume normal operation.

STS—Stop bit for all converter functions. When writing a '1' to this register, this bit aborts the converter function

currently running in the TSC2004. A '0' is automatically written to this register in order to end the stop bit. This bit

can only stop converter functions; it does not reset any data, status, or configuration registers. This bit is the

same STS bit shown in CFR0, but can only be read through the CFR0 register with different interpretations.

Table 8. STS Bit Operation

OPERATION

VALUE

DESCRIPTION

Write

Normal operation

Write

Stop converter functions and power down

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