Touchscreen not responding:
Problem: Touchscreen is not working.
TST350MLQZ-06P LCD with touchscreen (I tried two different units)
SSDD2219 SPI interface for display driver (SPI)
STMPE811 driver for touchscreen (I2C)
On a previous prototype board using the PIC32MX, we had the LCD and touch fully working. We needed more capabilities on the PIC so we changed processors.
The LCD display works fine. the touchscreen does not. I can write/read to both the SSD2219 and the STMPE811. I can read back, thus confirming that I can configure the driver chips. The STMPE811 handles the touchscreen. There are a series of registers that it uses to configure and capture touch activity. There is an interrupt, which is configurable. We use it when the FIFO contains a touch response.
I do not receive the interrupt on the PIC. When I scope the pin, I do not see any activity when I touch the display. So, it isn't the PIC. the STMPE811 is not generating the interrupt.
From the PIC, I also read the STMPE811's FIFO and status. There is nothing.
I checked the control related pins on the LCD display and they are seemingly fine. The only thing I found a little od was the Backplane voltage was only 5.4volts.
I then checked the 4 wire touchscreen interface. When I touch the display, I see no change in state for any of the pins. X+ is 3.3 volts. Y+ and X- exhibit similar signals. They are roughly zero volts, but you can see tiny periodic spikes down to -0.1 volts and +0.17volts. Y- is -0.02 to -0.1 volts.
I don't know if those are normal readings, but I would naturally and unknowingly think Y+ would also be 3.3volts.
Any help in debugging would be greatly appreciated. What readings should I expect on the 4 wire interface pins? I am guessing the power supply for the analog portion of the display provides the power. But, heck, I don't know.
Is it possibly a configuration issue with the STMPE811 touch driver. I am the software guy and I think it is a configuration issue. But, this configuration worked on the previous board.
I am stumped.
Thanks for any help I received,