I2C bus

Rene Kint · Post by **Rene Kint** » Thu Jan 13, 2022 9:36 am

Hello, all here. Not an expert on this, so might sound as a stupid question. You are warned ? . In the Programming guide I saw that there is an I2C bus in the system, but it also said that the RTC and the Sytem Management Controller are connected. I also saw there is a VIA#2 that is...unused?

Now, I would LOVE to have an I2C bus exposed from the X16 (to communicate with all kinds of hardware). Would that be a possibility you think? I don't think it is connected to the user port.

Looking forward to your expert answers!

R.

StephenHorn · Post by **StephenHorn** » Thu Jan 13, 2022 7:07 pm

Right now, I'm not aware of any general-purpose access to the I2C bus that will be exposed. VIA#1 will be used to communicate with the RTC and SMC, using I2C protocol, but I don't know of any other I2C access or components on the system. (Note that the plan seems to be to run the keyboard and mouse through the SMC, so querying those for state would happen via I2C. This is because the team has had problems maintaining stable PS/2 communication straight through the VIAs.)

Wavicle · Post by **Wavicle** » Thu Jan 13, 2022 9:26 pm

The render of the Rev 3 board shows this 6 pin header labeled "I2C" adjacent to VIA #1. Interpret that as you may. I'm not sure why the header is 6 pins.

BruceMcF · Post by **BruceMcF** » Mon Jan 17, 2022 8:23 pm

One conceivable reason for six pins would be for +5v/GND and +3.3v/GND.

Ed Minchau · Post by **Ed Minchau** » Tue Jan 18, 2022 1:07 am

Another reason: one pin isn't used, a 2x3 header is cheap.

BruceMcF · Post by **BruceMcF** » Tue Jan 18, 2022 8:10 pm

On 1/17/2022 at 8:07 PM, Ed Minchau said:

Another reason: one pin isn't used, a 2x3 header is cheap.

Yeah ... also, they are also using one for the SNES gamepad header, so using another instead of a 2x2 simplifies the BOM and reduces the possibility for mistakes in building.