I2C-1 vs I2C-0, SH1107 OLED

[pottendo]

Hi fellow-hackers,
in my application I can successfully access a SH1107 based OLED Display (this type here) when connected to I2C-0 - i.e. pins 27/28.
When I move this to i2C-1 - pins 3/5. The display won't work on a Pi3B+ and it works with obvious issues on a Pi4.

The lower part may be a driver issue - but the upper part of the picture is broken on the lower side.

I've tried initializing with both modes: mode == true and mode == false - no difference.
m_I2c = new CI2CMaster(BSCMaster, mode);

ChatGPT suggest this:

Can this really be the reason? I'm not very familiar with I2Cs so any advice would be much appreciated.
Can I break the Pi following the suggestion? Or, better, can I activate a PullUp via Circle? (as I do for some Pins in my application for button inputs, using the GPIO class).

thanks, pottendo

PS: Note that I've reused a hand-crafted I2C driver for SSD1306 which actually works nicely on I2C-0. However the driver just shows the symptom better - When i use the pure circle functions, like the constructor above and then read a single byte from the correct address (0x3C in my case) it fails on the I2C-1 but works on I2C-0. This implements a simple i2c scan - see linke below.

PPS: my project can be found here. i2C funcs are around here

[pottendo]

Hi,
I assume I found the answer: https://learn.sparkfun.com/tutorials/i2c/i2c-at-the-hardware-level
The question remaining here: can I activate a PullUp on the I2C-1 data/clock lines on the Pi?
thanks & happy hacking, pottendo

[rsta2]

According to this comment in the Raspberry Pi forum, there are already 1K8 pull up resistors for I2C-1 on-board of the RPis, which can't be disabled. I assume this is not the case for I2C-0. So if the display has pull up resistors too, the total resistance for I2C-0 is OK, but may be too small for I2C-1. Just an idea.

[pottendo]

Thanks,
I think, I need to find out first, if the display has some pull-ups or not... before toasting the Pi!
bye, pottendo

[pottendo]

Hi,
I've verified that my display has 10kOhm resistors installed (1k + 10k) - as my application can choose the I2C, I won't modify the OLED HW to try.
Problem solved (for me), thx, pottendo

PS: here the circuit: