Serial Out from PIC to PC without a driver?

Discussion in 'Embedded Systems and Microcontrollers' started by spinnaker, Jan 3, 2010.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    Last edited: Jan 3, 2010
  2. AlexR

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    Jan 16, 2008
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    The PIC can't supply RS232 levels without a driver, however the PC is a Microsoft designed device and so does not conforming to any established standards. It will therefore accept logic level signals on its com port.
    The main reason for using an RS232 driver with a PIC USART when talking to a PC is to invert the signal. The RS232 standard specifies a mark condition as -12Volt and a space as +12Volt, the USART outputs a logic 1 (5Volt) for a mark and logic 0 (0Volt) for a space.
    The project gets around the inversion problem by not using the PIC USART and writing its own comms program with the level inversion built into the software.
     
  3. spinnaker

    Thread Starter AAC Fanatic!

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    Wow that seems an awful lot of trouble to save buying a chip! :)


    I had a similar problem years ago. I had an Atari 800 and BBS had just come on to the scene plus I was going to college and I has able to do this most amazing thing of dialing up and connecting to our mainframe to do my homework.

    Someone had given me an old acoustic coupled modem but Atari had a modified SCSI out and no RS232. You could purchase an RS232 interface for $100 or so but I did not have $100 or so. I went to Rat Shack (back in the day when they carried most things) and purchased a couple of Rs232 line drivers and receivers. I then wrote my own device handler in assembler and was up connected to want was to become the world wide web in no time.

    Atari made building the device driver easy. That was a great OS. Can't remember how I got around device IDs, My interface was dumb and most others had some intelligence to them by announcing their device ID. I may have been able to write that into the driver. Can't rememebr for sure.
     
  4. t06afre

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    May 11, 2009
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    How stable/deterministic is such a system? I for sure would never have designed a RS232 system without proper RS232 signals levels.
     
  5. n9352527

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    Oct 14, 2005
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    It might work, it might not. I had a desktop that won't talk to such circuit. And two old laptops that would. Not something that I will put in commercial products.
     
  6. Markd77

    Senior Member

    Sep 7, 2009
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    Should the label 3.3-5V read 12V? Or does this rely on the serial port working with lower voltages?
     
  7. Markd77

    Senior Member

    Sep 7, 2009
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    Just answered my own question. 12V would be outside the range of the input pin of the PIC.
     
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