How to implement LCD capacitive touch screen
There are two types of touch technologies, resistive and capacitive touch that are widely used in nowadays TFT touch screen. We have a post of “how to implement LCD display resistive touch function”. Here, we are showing an example of setting up and testing the hardware interface to capacitive touch LCD panel.
- Tango C48 is used to drive a Topway 5 inch capacitive TFT LCD touch screen
- STM32F103VCT6 is the host MCU
Tango C45's pins are connected with STM32 MCU GPIOs like below:
* A pull-up resistor of 2.2K is needed.
IIC Timing Diagram
Tango C48 write sequence
Tango C48 read sequence
- MCU sends start signal S, sends write address: 0XB8(Address_W) 1*
- MCU waits for Tango's ACK signal, MCU sends read/write register address
- In read mode, MCU issues start signal S again, sends read address: 0XB9(Address_R) 1*
- Read/Write data from/to selected register
- Read/Write finished, MCU sends stop signal N
1* Tango C48 address format: 7 bits address + read/write bit
See attachment for sample code.
- On Tango C48 initialization, need to set aside registers for power, interrupt mode, interrupt length
- Try to use less interruption, instead set up flag to convey information to front end
- When using RTOS, avoid using IIC analog time sequence to read/write data. Multi-tasks processing will mess up time sequence. Using register is a better idea.