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Wake Up Circuit for CORTEX using serial port

  1. Mar 31, 2013 #1


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    Hi all,
    I am making my first attempt at designing a microcontroller for an autonomous chemical sensor package for marine systems. Previously, we used a commercially available microcontroller made by a company called Persistor (http://www.persistor.com/pii/products/cf2.html), but now we are trying to design our own controller using a CORTEX LM4F 232H5QD (http://www.ti.com/product/lm4f232h5qd).

    We are having trouble designing a wake-up circuit for this controller, and would really appreciate some help. We would like to bring the CORTEX out of hibernation when any character is sent through the serial port. The CORTEX has to be in the low-power hibernation mode, where interrupts are not available on the IO pins. There is a "WAKE" pin on the chip that brings the chip out of hibernation when it is pulled low. My first attempt was to put a circuit like the one attached, but it did not work.

    Right now, we are leaning towards adding a MSP430, and using it to monitor the RX line, and then when it sees a character, then it triggers the WAKE pin using an IO pin. This is how the CF2 does it, and we are confident that it would work, but it just seems like a very complicated way to solve this problem. Does anybody have an idea for a simpler design for this wake circuit?

    thank you!!


    Attached Files:

  2. jcsd
  3. Apr 2, 2013 #2


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    Science Advisor
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    You need a Pull-Up resistor. Image from "www.ti.com/lit/ds/spms319g/spms319g.pdf" [Broken]


    Attached Files:

    Last edited by a moderator: May 6, 2017
  4. Apr 5, 2013 #3


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    Thank you!!

    That did it! Thank you for your help!

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