Pico Display Pack backlight woes

I’m having issues with the backlight control on my Pico display pack - it works, but it’s obviously much dimmer than it should be. White comes out gray, for example.

I tried futzing with the backlight pin - first driving it high, then PWMing it after looking at how the provided C++ libraries did it. Neither worked:

  • Driving high seemed to turn the backlight off.
  • PWMing the pin just produced the same low brightness, no matter how I configured it. Ditto for just not touching the pin at all or driving it low.

I am running it with the Pico keypad off non-standard pins, but I followed the lead of another project that managed to make it work, so I’m a bit stumped.

Other notes:

  • I found out just before making this post that I can reach the low-brightness state by simply connecting the backlight pin to ground. Unsure if that means anything?
  • I’m using Rust with rp2040_hal and the mipidsi driver, but I don’t think those are the source of the issue.

EDIT: Grounding pin 8 fixed it! I’m using jumper cables to connect the display, and I only hooked up the data and power pins like a moron. Do I need to ground any of the other pins, or am I good? Thanks :)