• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 33 subscribers
  • Views 128 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THVD1520: Incorrect UART reading

Xavier Ramon Vilamu
Prodigy 140 points

Part Number: THVD1520

 
I have two THVD1520DR connected to each other and with their 120 Ohm resistors at the ends. The problem I have is that the data I send is not received completely, that is, if I send a string of 8 bytes I only receive 4 to 6 bytes and the last byte is incorrect. Initially, I only received 4 bytes, but by making some changes to the configuration in the UART I have managed to get up to 5 bytes to me correctly. As a detail, I receive the first message correctly, it is from the second that I receive 5 correct bytes and one incorrect.
Does the THVD1520DR have any specific configuration in the detection of the UART that may be affected by the detection of the bytes?
Thanks,
  • 0
    TI__Guru* 78111 points

    Hi Xavier,

    What data rate are you using?

    What is the distance/length of the cable?

    Can I see a schematic of both THVD1520s?

    Can I get a scopeshot of the bytes being sent and received? (I'd like to see the Tx, Rx, and A-B math function on the receiver node all on the same scope plot)

    Xavier Ramon Vilamu said:
    Does the THVD1520DR have any specific configuration in the detection of the UART that may be affected by the detection of the bytes?

    No, generally you can just have two connected through a cable with termination. 

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 140 points

    Hello, 

    I test UART speed with 9600 and 115200 and I have the same problem.

    The cable length is very short, 30 cm.

    The schematic is this

    For example,

    sent:        0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07

    received: 0x00 0x01 0x02 0x03 0x04 0xFF.

    I lost the last 2 bytes and changed byte 6.

    If I change the frame length, the issue moves to the new length.

    sent:        0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x10

    received: 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0xFF

    Thanks, 

  • 0 in reply to Xavier Ramon Vilamu
    TI__Guru* 78111 points

    Your distance is pretty short so you probably aren't getting issues related to reflections.

    Honestly you could remove the 120 ohm termination resistors at that distance and probably get better signal integrity.

    The 470 ohm pull up and pull downs are pretty strong, I think you can change them to 1k and be fine.

    I don't really see any major issues that would cause your received data to end with 0xFF.

    I think we need to get a scopeshot and figure out if this is the THVD1520 causing the issue or if it's upstream/downstream.

    Just to verify, do you have any level shifters or anything that sits on the TTL side of the THVD1520?

    -Bobby