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MSP430F5529: UART communication with another processor

Sparsh Gupta
Prodigy 230 points
Part Number: MSP430F5529

Hi

I am trying to use the MSP430F5529LP to send AT commands[http://www.elecomes.com/images/upload/File/Dot%20AT%20command.pdf], the receiver is essentially a processor[MTDOT-915-xx]. Now the whole setup works wonderfully when using both the boards are powered by USB. However when I try to power both the boards using 3.3V external power source. It doesn't seem to work. Datasheet of both boards say that 3.3V would do? What can be a potential problem?

  • 0
    Guru 41995 points
    Do you have a ground connected between the boards?
  • 0 in reply to Keith Barkley
    Prodigy 230 points
    So I am powering the both the boards with same 3.3V source. So grounds of both the boards and the voltage sources are shorted. I have removed all the jumpers in the isolation block.
  • 0
    TI__Mastermind 41120 points
    Hi Sparsh,

    When you are powering with 3.3V external supply, what seems to be the problem? Are you able to observe any communication on the UART lines?

    Also, can you provide an image or drawing of your connections?
  • 0 in reply to Eddie LaCost
    Prodigy 230 points
    Hi

    Yes I see my RX and TX lines going up and down when I press RESET and MSP430 tries to communicate with the other processor evb[https://www.multitech.com/documents/publications/manuals/s000612_DB9.pdf - Page26]. My scope isn't good enough to capture full data stream, but I do see some activity.

    Connections. Image would be difficult.
    TX[Pin3.3 on MSP430] - Pin3[check above link for the schematic]
    RX[Pin3.4 on MSP430]- Pin2[check above link for the schematic]
    Vdd = >+ from power supply to 3v3 in J10 header in MSP430 and Pin1 of the other processor[check above link for the schematic]
    GND=>-ve from power supply to GND in J10 pin in MSP430 and Pin10 of the other prrocessor[check above link for the schematic]
  • 0 in reply to Sparsh Gupta
    Guru 95385 points
    What sort of power supply are you using? The note ("Important:") on page 21 suggests there isn't much margin for droop at 3.3V in.

    When you're powering by USB, are you powering them independently? Or are you running the mDot board off the Launchpad?

    Does the Rx line into the MSP430 read high (3.3V)? If not, that suggests that the mDot isn't starting up at all.
  • 0 in reply to Bruce McKenney
    Prodigy 230 points
    With bench power supply, the setup works. However, I am trying to power up the device using a TEG power source, that doesn't work. What is the margin of voltage doop at 3.3Vin. I couldn't find anything in this datasheet - www.ti.com/.../slau533d.pdf

    When powering by USB,I am powering the mDot board using the launchpad 3.3V out.

    If I power the launchpad with 5Vin istead of 3.3Vin, will there be a difference in power consumption?
  • 0 in reply to Sparsh Gupta
    Guru 95385 points
    That note on page 21 of the mDot data sheet seems to say the margin of (voltage) droop at 3.3V in is 0.0, i.e. if the power supply drops to 3.29V the mDot won't function. The MSP430 will be perfectly happy with supply down to about 2V.

    I expect a power supply fed by the USB (or a benchtop supply) is pretty stiff; a TEG maybe less so.

    I'm not quite sure what you have in mind with the 5V pin, but as I recall on many/most Launchpads, powering through the 5V pin doesn't accomplish anything. (Check the schematics.)
  • 0 in reply to Bruce McKenney
    Prodigy 230 points
    Thanks a lot Bruce, you pointed me in th right direction and I have constructed a regulator circuit and I think my problem is solved.

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