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Problem with sci_echoback example program!

Dror Medini
Prodigy 190 points

Hello,
 
I am using CCS3.3 and I download from TI's site: sprc530 - which is the DSP2833x HeaderFiles & Examples SW. I am running the program sci_echoback with the supplied HyperTerminal File named SCI_96 and it works fine. Then, in the DSP2833x_Examples.h file, I changed the variant DSP28_PLLCR from the default value 10 to 8 (attached a picture: pic1)

I Built, Reset the CPU,  Loaded  and Run the program, but the communication with the HyperTerminal stopped working. I would like to highlight that this is the only change I made!

 

Maybe it has something to do with the scia_echoback_init() function (attached a picture: pic2).

  

I am using F28335 controller with a 30MHz crystal. However, after I changed DSP28_PLLCR from 10 to 8 the system’s clock changed to 120MHz (and not 150MHz). Maybe it somehow affected the BAUD. Anyway, I tried to change the SciaRegs.SCILBAUD register to smaller values but it did not help. Please help me!!! What should I do???

  • 0
    TI__Intellectual 3000 points

    Dror,

    The Baud rate would seem to be a good place to start troubleshooting after changing the PLLCR value. You can either reconfigure the baud rate manually by calculating it or can use the "auto baud detect" feature on the SCI peripheral. The document sprugh1c.pdf should be able to help guide you with this. There a register SCIFFCT which control auto baud detection, which by default is off. You will need to comment out the written code for the baud registers and establish auto baud detect. To do this:

    - Establish a known value '1' in SCILBAUD

    - Enable auto baud alignment (CDC) and clear the auto baud detect flag (ABD CLR)

    - Wait for (ABD) to go high - this register will go high once you send an 'a' or 'A' through the terminal to the receiver

    - Baud register should now be set, clear the auto baud flag again and disable auto baud alignment again.

    Again, the document http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=sprugh1c should be able to help guide you with this. If you would like to calculate and set the baud rate manually, also reference the guide to help you calculate what register values you will need.

    Hope this helps.

     

    Nishant

  • 0 in reply to Nishant Garg
    TI__Guru* 87155 points

    Dror,

    When system clock is 120MHz, LSPCLK is 30MHz (at default LSPCLK = SYSCLKOUT/4 and SCI_echoback example in headerfiels does not change the default LSPCLK settings).  So, when you calculate BRR using the formula given in reference guide, you need to use LSPCLK value of 30MHz (when sysclk is 120MHz) and not 37.5MHz.

    Regards,

    Vamsi