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C6748 LCDK Hardware problem: J15- pin: 2, 16, 20, 26, 40, 44

Petr Duga
Intellectual 495 points

In my project I need to do the software emulation of SPI.

I use the pins16 (GPIO8-12), 20(GPIO8-10), 40(SPI1_SCSn_1) and 44(SPI1_SCSn_0) for SPI emulations and 2 and 26 for VDD and GND of expansion connector J15 for this purpose. These signals, 3V3 and GND are connected with my breadboard, where are isolated using digital isolator ADuM1400. I had issues with correct function of that pins. After some time begin my application to behave strange I find out, that it is because one of pins used is defect. I buy another LCDK and tried again. It works, but after some times the pin issue happens again but with other pin. I buy another one and now I find out, that the the pin 2(VDD) copy the signal from pin 20 (GPIO8_12).

I used A5 and A6 versions of LCDK.

Does somebody have the some issues with pins of J15?

If so, where was the problem and what was the solution?

How can I use pins of J15 correctly?

Do you have an idea where to find layout of components of C6748 LCDK? on wiki was just schematics and gerber files, but for problem analysis it is good to have a components layout on LCDK in .pdf too.

Thanks for your answers, I attached the realized scheme and the picture of connection (the important part is the connection with LCDK).

Petr Duga

  • 0
    TI__Mastermind 43660 points

    Hello Petr,

    Could you please respond to the below questions.

    I use the pins16 (GPIO8-12), 20(GPIO8-10), 40(SPI1_SCSn_1) and 44(SPI1_SCSn_0) for SPI emulations

    Are you intended to use these pins as Serial interface ? If so why did you use SPI CS pins for data and clock ?

    I had issues with correct function of that pins. 

    What is your expectation on these pins functionality ?

     I find out, that it is because one of pins used is defect.

    How did you find out one of the pin is defect ?

     I find out, that the the pin 2(VDD) copy the signal from pin 20 (GPIO8_12).

    Do you mean the pins 2 and 20 are shorted with each other ? How did you verify this ?

    I checked the connectivity of J15.2 and J15.20 and i don't see any short over them.

    You can find the PCB layout files (section 5.2.1) in the below link. 

    http://processors.wiki.ti.com/index.php/L138/C6748_Development_Kit_(LCDK)#Hardware

    Regards,

    Senthil

  • 0 in reply to Senthilkumar Srinivasan
    Intellectual 495 points

    Hi Senthil,

    thanks for your answer.

    To your questions:

    "I use the pins16 (GPIO8-12), 20(GPIO8-10), 40(SPI1_SCSn_1) and 44(SPI1_SCSn_0) for SPI emulations

    -Are you intended to use these pins as Serial interface ? If so why did you use SPI CS pins for data and clock ?"

     

    Yes I wish to emulate SPI communication with included signals: MISO, SCLK, FSYNC  for setting registers of AD5932 (direct digital synthesizer) and special signal CTRL for starting generation of harmonic signal on AD5932. I use all above mentioned pins as GPIO pins and emulate SPI in my software, so it was purely random decision to choose SPI CS pins for data and clock. I find out, that I can not use SPIO in my HW specification.

     

    "I had issues with correct function of that pins.-

    What is your expectation on these pins functionality ?"

    In my software as a test sequence I sent in while loop ones and zeros successively on each of pins and measured the outputs from J15 on breadboard with scope. Expectation was: if 1 is sent 3V3 is measured, if 0 is sent cca 0V is measured.

    "I find out, that it is because one of pins used is defect.

    Do you mean the pins 2 and 20 are shorted with each other ? How did you verify this ?"

    I found out, that it was because of bad connection of wires on breadboard.  Pins 2 and 20 was probably connected together via capacitive coupling. I have changed wires and now this is not an issue for me.

    In previous cases however there was an issue with the defect pins. I tested those pins with the sequence of 1's and 0's and measured the output voltage on breadboard. In one case there was no change on output of tested pin and in another case there was not change between 0-3V3 as expected, but only cca 1V2-3V3.

    Do you know Senthil what are the maximum electrical ratings of those pins? Or could you point me to the document where can I find it? I don' t know where was the poblem. I solved this issue by using digital isolator ADUMC1400 and it seems to work.

     

    Thanks for your answers.

    Best regards

     

    Petr Duga

     

  • 0 in reply to Petr Duga
    TI__Mastermind 43660 points

    Hello Petr,

    Thanks for your response.

    In one case there was no change on output of tested pin and in another case there was not change between 0-3V3 as expected, but only cca 1V2-3V3.

    This might have been due to ground issue. Did you check the output at J15 connector pins without connecting your custom board. 

    You can refer the C6748 datasheet chapter 5 for electrical specifications.

    http://www.ti.com/lit/ds/symlink/tms320c6748.pdf

    Glad to know that you solved the issues that you faced by using digital isolator.

    Please note when you ring up the circuit using breadboard, ensure the wires are properly connected and power/ground connections are proper.

    Regards,

    Senthil