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3705 and 37157 communiction error rate

du lili
Prodigy 50 points
Other Parts Discussed in Thread: TMS37157

I  am designing a wireless system with 3705 and 37157.

The testing distance is about 2cm,and the antennas are provided by the EZ430-TMS37157 .In msp access mode,the data back from 37157 is at an error rate about 2%.I tested the waveform with oscillorscope,the SPI read and write back to 37157 is right,but the scio waveform is really wrong.For example,I send 6 bytes as :04 01 a5 5a 01 0a,but the returned value may be 04 01 85 5a 01 0a  or 04 00 a5 5a 01 0a,or other.   The wrong pattern is always altering bit '1' to '0' ,and never '0' to '1'.

What is the reason ? Is the wireless communication unreliable ?

Thank you very much,and hope for reply anxiously!

  • 0
    Prodigy 50 points

    nobody tells me?

    where are  TI's engineers ?

  • 0
    TI__Mastermind 44140 points

    Hi Du,

    Please take a look at the attached training presentation.  Page 22 describes how to interpret the bits based on the TXCT and SCIO relationship.  Be sure that you are rotating the bits and then performing ones complement so that you are interpreting the bits correctly.

    When you see the wrong data, are you receiving a CRC error as well?  If the transponder is right on the edge of the read range, you could receive a CRC error.  With the eZ430-TMS37157, 2cm should be fine if the transponder antenna is in the correct orientation as pictured on the first page of the training document.  If the transponder antenna is rotated 90 degrees, the coupling is not optimal and may be out of range or on the edge.        

     

    TMS37157 PaLFI_Technical_Training_03_22_2010.pdf
  • 0 in reply to Eddie LaCost
    Prodigy 50 points

    Eddie LaCost:

                     Thank you for your reply.

                     (1)The relation of TXCT and SCIO has been noticed by me,the basestation firmware is based on the EZ430-TMS37157 demo.And if SCIO is not reversed,all bits received are reversed,but my wrong data is only wrong at one or two bits.

                    (2)Yes, CRC error. I compared the wrong data with right data.The CRC are the same,but data are changed.So It seems that the error happens during the transmission process.

                    (3) The distance is within 2cm of the transmitting antenna,and the coil directions are guaranteed in parrallel.

     

                    Any suggestions,Eddie LaCost?

  • 0 in reply to du lili
    TI__Guru* 91206 points

    Du -

    can you check your hardware setup? are you using the EVM or your own boards. if you are using your own devices, then tuning/trimming might be needed on the TMS37157 side. If you are using the EVM, then if you could share any 'scope shots that you have taken (similar to what we have shown in the slide deck Eddie sent) with TXCT, SCIO and the carrier relationship all together on one screen here.  

  • 0 in reply to Josh Wyatt
    Prodigy 50 points

    Thank Josh Wyatt for your reply!

          Now there is some advance.According to the following  webpage,I added some delay in my transponder firmware,means add some delay in the spi communiction.Now the result is that there is error yet,but the error data becomes all 0,means 37157 does not transmit response data .So it is really an issue about the EEPROM writing,but where should I put the delay.I tried to put the delay somewhere,but there is no a place for me to avoid the all 0 data absolutely.

        Could you give me a suggestion ?You may tell me firmware changes based on the transponder firmware inclosed in the EZ430-TMS37157,because mine is based on it too.

        Thank you very much!

     

    http://e2e.ti.com/support/low_power_rf/f/155/p/87885/303792.aspx#303792

  • 0 in reply to du lili
    TI__Guru* 91206 points

    Before you change the FW, can you answer my questions about your hardware and how you are capturing events and how you can share this data?

    thanks!

  • 0 in reply to Josh Wyatt
    Prodigy 50 points

    Thank Josh Wyatt   for your reply.

    The hardware is mine.Now I think I  have found the problem.The main problem is at  the 3705 receiving circuit.

    I use my  mcu to output TXCT and SCIO ,and TI demo's 3705 and 27424,the result is ok,no error rate. So the problem is hardware. I checked the circuit placement,the 3705 is far from the antenna, so the response to 3705 is very weak and easy to be influenced. But TI demo's circuit placement here is very good. So I think this is the reason.Do your agree ?

    Do you have any PCB suggestions on 3705 and 37157 ?

    Thank you!