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SCI A Stays logic high

Trevor Horst
Prodigy 30 points

Other Parts Discussed in Thread: CONTROLSUITE

I've been trying to get the SCI A port to work properly for quite some time and I've only had minimal success. I've read through a couple of the posts on this forum and they all seem to just point to the controlSUITE example which works just fine in the case of a loopback use. However, I am attempting to get the piccolo communicating with a PixyCam (CMUCam5) and I've noticed that the SCI A Rx line remains high. Thus when transmitting, it results in a situation where when the PixyCam sends data the bit only causes a change of about .2V. I assume this is the reason why I have been unable to see what the PixyCam has been sending. 

In short, my receive line remains logic high constantly and I believe it is causing transmission errors. Is there a way to drive it low or am I missing something here?

  • 0
    Guru 192875 points

    Hi Trevor,

    First of all, which controller & compiler version are you using? Secondly, have you tried out the SCI_echoback example? Does that work as expected?

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Prodigy 30 points

    Oh, my apologies! The controller is the T28069M Piccolo, and I'm using CCS v6.0.1 (Not sure which compiler this uses by default) And yes, I've tried both the echoback and the loopback. When tieing the Rx line directly to the Tx line it works just fine and I can see the input/output coming through the terminal just fine.

  • 0 in reply to Trevor Horst
    Guru 192875 points

    Trevor Horst said:
    Oh, my apologies! The controller is the T28069M Piccolo, and I'm using CCS v6.0.1 (Not sure which compiler this uses by default) And yes, I've tried both the echoback and the loopback. When tieing the Rx line directly to the Tx line it works just fine and I can see the input/output coming through the terminal just fine.

    That's great! Atleast we're through with basic SCI config. now with the slave CAM device, are the baud rate and other configurations matching?

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Prodigy 30 points

    Yeah that part took some doing. Using a DSP28_DIVSEL of 1, I believe this sets the SYSCLKOUT at 90mHz (Clock speed / 1 ) and setting the LOSPC bits to 3 to set up a 15mHz (SYSCLKOUT / 6) clock. Which I then used the formula from the reference manual and I calculated a value of 0xC2 for 9600 baud at that clock rate, which matches up with the suggested value in the manual. The camera is also programmed for 9600 baud.

  • 0 in reply to Trevor Horst
    TI__Guru 55700 points

    Trevor,


    Have you ruled out hardware issue. I wondering whether SCIRX pin is somehow shorted to 3.3v.

    Regards,

    Manoj