DFR0669 + GT911 touch chip -- can't get interrupt to work?
Casey.Connor 2023-11-08 18:36:20 505 Views3 Replies Hello – I can not get the interrupt mode to work with the touch screen controller chip GT911 on the DFR0669 display module (with ESP32-DevKitC-VIE).
It works fine in polling mode.
I have tried four or five different libraries, and I have also manually set the interrupt mode registers (0x804D Module_Switch1, last couple bits) but nothing happens on the INT line no matter what I do.
I am starting to wonder about something: from the GT911 datasheet (pages 18 through 20), it sounds like VDDIO might be as low as 1.8V, depending on the configuration and external circuitry around the chip. If VDDIO is 1.8V, then the max output voltage on INT is 1.53V, and this won't be enough to trigger a 3.3V GPIO pin. (I don't own an oscilloscope or I would confirm this.)
Does anyone know anything about the VDDIO level on the DFR0669's GT911 chip?
Does anyone know what the INT max voltage is?
Has anyone got this display module touch screen to work in interrupt mode?
This is the display module schematic – I'm not sure what U2 is, but the INT line passes through it?
Thanks!
The more I look at that U2 chip, the more I think my low-voltage idea might be correct… the touch screen is sending CTP_INT to the input of the U2 chip running at 3.3V, and if I am interpreting the CD74HC4050PWR data sheet correctly that means U2 is expecting about 2.4V for a HIGH and it's probably getting 1.53V (if VDDIO is floating on the GT911).
And that would in turn mean that I won't see anything, even 1.5V, at the “INT” pin on the screen module, right?
If VDDIO is tied to the 3.3V rail, though, I would expect signal at INT…
Casey.Connor Update: The U2 chip from the display schematic seems to be a TI CD74HC4050PWR (https://www.ti.com/product/CD74HC4050/part-details/CD74HC4050PWR) which seems like it might be doing the level shifting between VDDIO and 3.3V? Just a shot in the dark, but it makes my theory a little less likely…
Casey.Connor I don't know why all the links were stripped out of my post. Let me try again:
GT911 Datasheet: https://www.distec.de/fileadmin/pdf/produkte/Touchcontroller/DDGroup/GT911_Datasheet.pdf
DFR0669: https://wiki.dfrobot.com/3.5inches_480_320_TFT_LCD_Capacitive_Touchscreen_SKU_DFR0669
Casey.Connor 
