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CCS/TM4C129ENCPDT: RS485 in high temperature

Susan Yang
Genius 9955 points
Part Number: TM4C129ENCPDT


Tool/software: Code Composer Studio

Dear team


   The cpu is 3.3V working voltage and working current is 200mA.

Then set temperature to 68℃, humidity bit 0,

The 485 communication of the customer's CPU board has the phenomenon of turning on and off one frame.

Please help.

02 03 00 3c 00 01 44 35
02 03 02 00 02 7d 85
02 03 00 46 00 01 65 ec
02 03 00 46 00 01 65 ec
02 03 02 13 88 f1 12
02 03 00 83 00 06 34 13
02 03 0c 00 02 00 34 00 34 00 34 00 34 00 01 f9 01
02 03 00 3e 00 04 25 f6
02 03 00 3e 00 04 25 f6
02 03 08 00 00 00 00 00 00 00 00 9a 93
02 03 00 44 00 01 c4 2c
02 03 02 00 00 fc 44
02 03 00 00 00 06 c5 fb
02 03 00 00 00 06 c5 fb
02 03 0c 01 e3 01 e2 06 40 06 40 00 00 00 00 34 13
02 03 00 06 00 0a 25 ff
02 03 00 06 00 0a 25 ff
02 03 14 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f7 82
  • 0
    TI__Guru**** 191906 points

    Hi Susan,

      - There is not enough information for me to understand the problem. Are you saying at lower temperature below 68C then everything is fine?

      - I cannot decipher the data stream in the rs485 communication? What is wrong? Which frame is missing? Can you highlight it?

      - The current seems high at 200mA, much higher than the max listed in the datasheet. What is the operating frequency and how many modules/peripherals are running at the same time? 

      - How many boards do you see the same problem? What is the percentage? If it is only one board, you might want to check for any shorts on the board or bad soldering. 

  • 0 in reply to Charles Tsai
    TI__Genius 9955 points

    Thanks for your reply.

    1  200mA is the total current of the CPU board

    2 At 68℃, the serial port is always a frame of normal communication, and then the communication is disconnected for one frame.

    3  The serial communication returns to normal when temperature returns to 66°C

  • 0 in reply to Susan Yang
    TI__Guru**** 191906 points

    Hi Susan,

      What about my fourth question? Is this an occurrence on one board or multiple boards?

  • 0 in reply to Charles Tsai
    TI__Genius 9955 points

    They test 5 boards, 3 of them have this phenomenon

  • 0 in reply to Susan Yang
    TI__Guru**** 191906 points

    Hi,

      So some boards are ok. I tend to think it may have something to do with the system/board design. At 200mA, it way exceeds the limit given on the datasheet. I cannot believe the problem is with the MCU. I have some more questionns.

      If the RS485 is not operating, what will the current?

      How long is the RS485 bus length?

      Is there a reset or anything when the problem occurs? They can check the reset cause register.

      I assume they are using the UART module for the RS485, correct? Are there any errors from the UART module? Can you show the scope capture? 

      What and how many modules are operating? 

      Can you also ask your customer to go through the TM4C system design guideline. Check if they have sufficient decouple capacitors on the VDD and VDDC. 

    https://www.ti.com/lit/an/spma056/spma056.pdf?ts=1595075774242&ref_url=https%253A%252F%252Fwww.google.com%252F