7" Touch Display I2C pin connections

[JimmyN]

I followed this https://www.raspberrypi.org/blog/the-ea ... i-display/ to get the display up and running. I used the GPIO option to power the RPi, connecting the 5V & GND on the display's I2C connector over to pins #4 and #6 on the RPI. But the blog only shows the power pins in use, with no connection to SDA, SCL.

I had assumed that the I2C connections on the display interface were for the touch screen, so I went ahead and connected them up at first. But I have found that touch works whether they are connected or not. I currently have SDA and SCL unplugged and everything seems to work the same.
So should they be connected, or are they for some feature I haven't yet discovered?

[dgordon42]

See this.

The I2C Bus data runs through the Display Connector on the A+/B+ & 2B model Pi's.
There is no I2C Bus connections in the Display Connector on the A & B models.
The 'spare' I2C pins on the display module are there to allow a fix to be developed so that the display can be used with the A and B models.

Dave.

[JimmyN]

Thanks, that makes sense.

[Rob73]

Using other-i2c-devices with the Official 7" Touchscreen

If my understanding is correct, then the Touch-Input of the Official 7" Touchscreen uses i2c to communicate touches to the Raspberry Pi.

In the RasPi-2B and RasPi-3B (at least), the Official 7" Touchscreen seems to use i2c-0, which is passed through the ribbon "Display Connector". Thus is appears that i2c-1 on these versions of the RasPi is still available on the GPIO pins for other use: I have successfully connected a DS3231-RTC to the GPIO_i2c-1 on my RasPi-2B and RasPi-3B, and the touch-functions of the Touchscreen continue to work fine.

[I would postulate that on the original RasPi-A and RasPi-B that the Touchscreen still uses i2c-0, but on these original RasPi's this is the same i2c-0 which is on Pins #3 & #5 on the GPIO (to which on these original models you have to use jumper-wires on the GPIO SDA & SCL to connect to the Touchscreen). Which means that you can't use this GPIO i2c for anything else on these original RasPi-A & -B, UNLESS (perhaps) you disable the touch-functions of the Touchscreen (eg. by putting "disable_touchscreen=1" in config.txt, and also disconnecting the i2c-jumper-cables) - which MIGHT allow you to then use the GPIO i2c for something else on these original RasPi's??]

If anyone could confirm the above is correct, it would be appreciated!?!

Update (23Mar): Many thanks for concise reply!

[6by9]

Yes, your understanding is correct.

A+, B+, 2, and 3 all use i2c0 for configuring the display and touchscreen. I2c1 is still available for other uses.

A and B need to use the other i2c bus for the display via additional wires - whether that is 0 or 1 I think varies between revisions.