Comment by jauntywundrkind
2 months ago
I know it's called a bus, but I'm still surprised that all devices get the HDMI-CEC stream of all other devices. Being able to watch the Apple TV from the Pi was super cool, and I never would have guessed it was possible to see what was going on there (short of building a man in the middle hardware proxy)!
CEC is just i2c which is a bus. In fact you can hook regular i2c devices up to an HDMI port and communicate with them. You’ll need a resistor and shouldn’t draw more than 50 mA.
I always assumed that it was a separate i2c bus per HDMI link and that it was the AVR’s job to handle a request from something and send the right requests to everything else.
Much like i2c, any message put on the bus is transmitted to everything on the bus.
Version 1.0 and later of the HDMI spec even mandate that you have to connect those pins across all HDMI ports on your device even if you don't do anything with them.
3 replies →
Isn't DDC the I2C bus? Interesting article about that here: https://mitxela.com/projects/ddc-oled
Doh, you’re right. I’m over here getting my protocols mixed up. IIRC it is very similar though.
It's electrically similar, but not directly compatible. (if you know better than me, please let me know)