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I2C SDA rise time

Maor Matityahu
Intellectual 610 points

Hello,

In the I2C i have MCU as master, FPGA and 3 more components as slaves. I have 5kohm pull up resistors. In the SDA i see somtimes diffrent rise times when the MCU send the address to the FPGA.

Yellow - SDA

Green - SCL

good SDA pulse:

Not a good SDA pulse: Slow rise time and less high level of the SDA (this is the second pulse - the pulse after the picture above):

Why is that?

Thank you

  • 0
    TI__Guru 71526 points

    Hello Maor, 

    Please provide more information - is the MCU driving the I2C bus directly and if so, what MCU?  

    If there is a buffer between the MCU and the I2C and if so, what is the device? 

    And in the second 'scope capture you show with the slower rise-time, is that signal originating from the MCU, or one of the devices on the I2C bus?

    Thank you, 

    ~Leonard  

  • 0 in reply to LeonardEllis
    Intellectual 610 points

    Hi,

    The MCU driving the I2C directly without buffer. only 33ohm resistors in the start of the line and in the end of the line. and 5kohm pull up in the middle of the line.

    The MCU is of silicon Labs: EFR32BG24A010F1024IM48-B

    Yes i think the signals in the pictures are originating from the MCU since i see the address of the FPGA (MCU sends the address of the FPGA). The address of the FPGA is 1010000

    Zoom out pictures:

    Thank you

  • 0 in reply to Maor Matityahu
    TI__Guru 71526 points

    Hello Maor, 

    Since the SiLabs MCU is used, you will have to contact SiLabs for information.  

    Regards,

    ~Leonard