Figure 4.
Data Format
1.2.2
Touch control circuit
The touch control circuit is managed by the TSC2046. It is a next-generation version to the ADS7846 4-wire touch
screen controller which supports a low-voltage I/O interface from 1.5 V to 5.25 V. The TSC2046 can detect the
pressed screen location and measure touch screen pressure. The communication between the TSC2046 and the
external microcontroller is performed via SPI.
On the
evaluation board, every time the TSC2046 detects a touch on the display, it raises
an external interrupt to inform the MCU that a touch event occurred. Then, the MCU sends a request via SPI
communication to the TSC2046 to retrieve the X and Y coordinates related to the touch just detected. The
external interrupt is disabled and low during the measurement cycle for the X and Y coordinates.
Figure 5.
SPI communication protocol implemented by TSC2046
Note:
(1) For Y position, driver 1 is on when X+ is selected and driver 2 is off. For X position, driver 1 is off, Y+ is
selected and driver 2 is on. Y- turns on when power-down mode is entered and PD0 = 0.
Note:
(2) Drivers remain on if PD0 = 1 (power-down mode not activated) until the selected input channel, reference
mode or power-down mode is changed or CS is high.
In the figure above, the source of the digital signals is a microcontroller with a basic serial interface. The
communication between the processor and the converter consists of eight clock cycles. One complete conversion
can be accomplished with three-serial communication, for a total of 24 clock cycles on the DCLK input. The
first eight clock cycles are used to provide the control byte via the DIN pin. When the converter has enough
information, it enters acquisition mode.
The acquisition time is included in the first eight clock cycles while the next twelve clock cycles accomplish the
actual analog to-digital conversion. In
, the TSC2046 is configured to complete the conversion
in thirteen clock cycles. To complete the D
OUT
replay message, three more clock cycles are needed but they will
be ignored by the converter.
UM2939
Hardware overview
UM2939
-
Rev 1
page 4/28
