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J
jesse-CST
Associate
November 17, 2024
Question

Addind Delay between I2C Master to Slave Address Send and Data for Read Operation

  • November 17, 2024
  • 3 replies
  • 1594 views

Hello,

I am interfacing with a sensor via I2C, with my STM32G0 MCU as the master. The sensor (Panasonic SN-GCJA5 air particulate sensor) requires a 500us delay between the I2C address read byte, and the data being read from that register:

 

jesseCST_1-1731875041718.png

This is definitely an uncommon requirement, but here we are. To be clear, this is not clock stretching. It appears the device expects a hard coded delay for some kind of internal processes to complete before data is available. I have tried without the delay, and sure enough no data from the sensor is presented. I have found other forum posts that have similar questions, with no answer yet:

https://community.st.com/t5/stm32-mcus-products/i2c-delay-between-address-byte-and-first-data-byte-when-reading/m-p/743724#M266420

https://community.st.com/t5/stm32-mcus-products/i-want-to-make-a-delay-between-the-slave-address-and-the-data-in/td-p/159249

I have gone below the I2C's HAL to see if there are register level manipulations that can make this possible, but I don't see a way to do it. Anything below byte level reads and writes seems to be abstracted in hardware. However I am not an STM32 I2C expert. Does anyone know of a clean way of doing this?

Generating a bit-bang I2C software interface is not an option for this design. 

Thank you.

3 replies

T
Techn
Senior III
November 23, 2024

you may have to use LL function to wait for LL_I2C_IsActiveFlag_BTF
Function name
__STATIC_INLINE uint32_t LL_I2C_IsActiveFlag_BTF (I2C_TypeDef * I2Cx)
Function description
Indicate the status of Byte Transfer Finished flag

 

I guess you can use the HAL_I2C function with a longer timer for timeout , the HAL function waits that much time before return with error code.

 

I2 C Status register 1 (I2C_SR1).BTF flag may be a solution.. 

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Pavel A.
Pavel A.
Super User
November 23, 2024

> To be clear, this is not clock stretching.

Have you checked SCL with a scope? From the picture, it looks just like the device may stretch SCL, before ACK for slave address.

S
szablas1001
Visitor II
May 6, 2025

Were you able to start the correct communication? If so, could I ask for a function to support the SN-GCJA5 sensor for stm32g0, I would be very grateful.

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