Hyperpixel 4.0 special GPIOs

Hi, based on this pinout for the Hyperpixel 4.0 Touchscreen, i have some questions:

  1. GPIO18(Chip Select): What does this GPIO mean? Is this one necessary?
  2. GPIO27(Touch Interrupt): What does this GPIO mean? Is this one necessary?
  3. GPIO26(LCD Program DATA): What does this GPIO mean? Is this one necessary?
  4. GPIO19(Backlight Control): This is a PWM Signal, right? Can i pull this signal up to 3.3V to always have full brightness?

Thanks for your answers

GPIO18(Chip Select): What does this GPIO mean? Is this one necessary?

The SPI bus needs a GPIO pin to tell a device when it is being communicated with. This allows SPI to use the same pins for data transmission with several devices without mxing up instructions, as only the device getting the Chip Select signal pays attention. So yes, definitely needed.

GPIO27(Touch Interrupt): What does this GPIO mean? Is this one necessary?

Interrupt pins are what they suggest: when something happens, this pin interrupts whatever the Pi is doing to get it to respond quickly to the event. In this case, it is used to make the touchscreen respond immediately to your finger touching the screen. If your Hyperpixel doesn’t have the touchscreen overlay then you don’t need it, although I’m not sure if the Hyperpixel library allows you to reassign it for a different function.

GPIO26(LCD Program DATA): What does this GPIO mean? Is this one necessary?

I can only assume that this is for sending data to configure/program the LCD controller chip, so yes, it would be needed.

GPIO19(Backlight Control): This is a PWM Signal, right? Can i pull this signal up to 3.3V to always have full brightness?

I assume so, but setting the screen to maximum brightness will probably do the same, and will be easier than trying to override Hyperpixel’s attempts to control the pin.

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I’m curious as to what you’re building, it looks like you’re after a GPIO (or 2) for something. From the product page:

  • HyperPixel uses basically all of the GPIO pins to communicate with the Pi (including the standard I2C pins) so it’s not generally possible to use it with other HATs and devices that connect via the GPIO…
  • …but we have provided an alternate I2C interface broken out on the back that will let you use I2C devices (like sensor breakouts) at the same time as HyperPixel.

The I2C would probably be your best bet. perhaps something like this?

Thanks. I analysed the Alt-Modes of the GPIO’s of my Raspberry. In the picture below, you see the results of the analysis. I used exactly this configuration to communicate with my touchscreen. Unfortunately, your Answer isn’t identical with the result of the GPIO analysis. For example, the GPIO18 is a Communication from the raspberry Pi to the Touchscreen, as you said. I only share this opinion with you. The analysis gave, that the GPIO18 is configured as an Input. How is this possible? Are there any plausible reasons?
Thanks

I do believe it used DPI, not SPI. Just something to keep in mind.