I2C between ST nucleo and AGX

[moti4]

Hi,

I’m trying to write a simple program that communicates via i2c pins 3 & 5 of the 40 pin expansion header with a ST development board nucleo-g071rb.
So the pin mapping is as follows with direct wiring (no resistors, AGX to ST):
3 → PB9 (SDA)
5 → PB8 (SCL)
9 → GND

The ST pins were configured for I2C1, low speed and with pull-up (to use internal resistors), all other parameters were left intact (including slave address, no dma etc.).
The micro program was developed in various ways (blocking slave / master with event interrupt disabled, interrupt mode with NVIC interrupt enabled).
However, using i2cdetect over bus 8 doesn’t yield any register indication and from the micro side it reports an error of HAL_I2C_ERROR_AF when trying to receive data (to work with read byte command of i2cdetect).
Tried other i2c buses, but no answer as well.

Am I missing something on the ST side for proper configuration of the board?

Thanks in advance,
Moti.

[JerryChang]

hello moti4,

you may see-also Jetson AGX Xavier Series OEM Product Design Guide for [Figure 13-1. I2C Connections].
they’re pin# A53/C53, and there’s voltage level shifter (1.8V or 3.3V). it’s by default 1kΩ pull-ups to 1.8V on module, please double check the device is using 1.8V also.

[moti4]

Hi Jerry,

Thank you for the pointer, it was helpful.
So apparently it is due to an electrical mismatch.
The specific board is NUCLEO-G071RB | Mbed (possibly to use NUCLEO-L476RG | Mbed).
It seems like it expects 3.3V on the I2C interface (from their header connection and datasheet).

Taking a look here, the guide describes how to connect two ST boards with pull-up resistors of 4.7 kOhm.

What would be the recommended approach?

• Hardware-wise to add the right resistance or level-shifter?
• Configure jetson registers as in note 2 Table 13-4? If yes, how can that be accomplished?

Thanks,
Moti.

[Trumany]

Hi, please check the jumper connector J514 on carrier board. It is for voltage level of I2C you used. Shorting pin 1 and pin 2 of J514 will set the I2C level to 3.3v.

[moti4]

Perfect, I’ll check that.
Can you guide me where in the documentation I can find more details about it? (For any future need).

[moti4]

Hi, following @Trumany suggestion that helped a lot, another modification was needed on the STM32 side.
Seems like working in blocking mode requires delicate handling, while interrupt mode was successful.
In addition, the project is configured without pull-up resistors.

For anyone interested, check out the following link: https://community.st.com/s/article/how-to-create-an-i2c-slave-device-using-the-stm32cube-library, and my original post here.