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Problem with sending data to GPS — Parallax Forums

Problem with sending data to GPS

SJSUprojectSJSUproject Posts: 3
edited 2007-03-23 00:13 in Robotics
I am using a Atmel Atmega16 microcontroller to send and receive data form the Parallax GPS module.· I am setting the baude rate at 4800.· I've followed the data sheet exactly for controlling the GPS module, however, it is not responding.

I've established communication with 2 microcontrollers w/ baude rate 4800 with no problem.

Is it possible that there is an issue with my GPS module??· If anyone is familar with this type of application, I would appreciate any guidance.· Please let me know if I can provide any more specifics.

Thank You.
Steve

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-03-18 03:26
    The bidirection communication needed for the GPS receiver may be a problem for the Atmega16. Not all serial I/O routines can provide this. It is always possible that your module is defective, but very unlikely. Most likely the problem is with the Atmega16's serial I/O routines and how they're configured.

    Briefly reviewing the Atmega16's datasheet, it's clear that the built-in USART is not really set up for this kind of bidirectional serial I/O. It can be done by disabling the Atmega16's transmitter as soon as the transmit buffer is empty. The receiver will echo the transmitted data if it's not disabled while transmitting. You may need a pull-up resistor on the I/O line as well. You could also implement this by using an open-collector or open-drain buffer for the Atmega16's transmit pin.

    Post Edited (Mike Green) : 3/18/2007 3:38:12 AM GMT
  • FranklinFranklin Posts: 4,747
    edited 2007-03-18 05:19
    I've established communication with 2 microcontrollers w/ baude rate 4800 with no problem.
    Is this with the same GPS module or MC to MC?
    What are you sending and what is it you expect to get back?

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    - Stephen
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-03-20 16:01
    I agree with Mike…The most common problems interfacing some of our peripherals to other controllers is that many don’t seem to support serial communication through a single I/O pin but rather have separate RX/TX pins. If you can use inverted baud mode you may be able to use the attached schematic to connect to the GPS Module. Take care.

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    Chris Savage
    Parallax Tech Support
    bmp
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    PC to GPS.bmp
    239K
  • SJSUprojectSJSUproject Posts: 3
    edited 2007-03-23 00:12
    Franklin said...
    I've established communication with 2 microcontrollers w/ baude rate 4800 with no problem.


    Is this with the same GPS module or MC to MC?
    What are you sending and what is it you expect to get back?

    We sent it MC to MC. We just sent a command to get Latititude as if it were the GPS.
  • SJSUprojectSJSUproject Posts: 3
    edited 2007-03-23 00:13
    Thanks all for the replies.

    On a side note, we are able receive GPS strings in unidirectional mode through MAX202.



    We are going to try the implementing the schematic. I'll update on what happens
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