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Electrical Noise Susceptibility — Parallax Forums

Electrical Noise Susceptibility

kt88seampkt88seamp Posts: 112
edited 2010-01-11 00:07 in Propeller 1
I have a propeller chip that is communicating with my PC via a FT232RL setup. How possible is it for noise to corrupt the transmission between my PC and the propeller? Should I put in any spin code to detect invalid data and correct it or does the FT232RL take care of all that? I have so far·not yet had any trouble with noise corrupting or interfeering with FT232Rl communication.

Post Edited (kt88seamp) : 1/10/2010 8:30:57 PM GMT

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-10 20:38
    The RS232RL does nothing to detect invalid data and certainly does not correct it. By converting the 3.3V logic levels to RS232 levels and slowing down the signal transitions from speeds on the order of nanoseconds to microseconds, it does make the transmission more robust and more resistant to electrical noise. Whether you need some kind of error detection and possibly error correction depends on the electrical environment, speed of transmission, and need for reliability. If you're sending character data (7 bits of data in an 8 bit channel), you can easily add even or odd parity to each character and check it on the PC side. That will at least tell you if some errors are occurring. If you're sending blocks of data, you can add a simple checksum or CRC at the end of a block. If you're seeing errors or you have a need for reliability, you can add the ability to request retransmission on a receive error. If you're using short range RS232, you might consider switching to wireless using xBee or Bluetooth since both these systems incorporate error detection and correction in a transparent way.
  • kt88seampkt88seamp Posts: 112
    edited 2010-01-10 20:53
    The RS232 part does not incorperate error correction but what about the USB portion of the line that runs from the PC to the FT232RL? The segment that transmits the RS232 data to and from the propeller is on a PCB and is only about .25 inches.
  • LeonLeon Posts: 7,620
    edited 2010-01-10 21:28
    It depends on how important the data are. A medical system I helped develop has a serial comms link to a PC. I implemented CRC error checking for each block of data with a protocol that requests a retransmission of the data if an error has been detected. An error log is maintained on the PC and there has never been a single error, apart from when I introduced them during testing.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM

    Post Edited (Leon) : 1/10/2010 9:34:46 PM GMT
  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-10 21:46
    @kt88seamp - The USB bus uses error detection and correction. Although it's possible for errors to creep into a 0.25 inch connection due to electrical noise, it's pretty unlikely unless you've got high voltage / high current transients running close by. More likely is an outright interface failure. As Leon said, it all depends on how important absolutely correct data are. If you're concerned, add even or odd parity. If you're really concerned, add CRCs.
  • kt88seampkt88seamp Posts: 112
    edited 2010-01-11 00:07
    Im not insanely concerned. More curious than anything [noparse]:)[/noparse]
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