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max232 pin states

Discussion in 'Electronic Design' started by DigitalBug, Jan 18, 2005.

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  1. DigitalBug

    DigitalBug Guest


    i feel stupid when i think what really happens at the r1out of max232
    when i send "1" by means of a vb program, out of rs232 into r1in of
    max232. any help will be appreciated.
  2. Paul Burke

    Paul Burke Guest

    I can't talk you through how it trickles down through the sewers of the
    Windows drivers, but once it gets to the MAX232, the first thing that
    happens is that the input R1in (if that's connected to the output of the
    UART) goes low for one bit period (i.e. 1/(Baud rate)). '1' is 0x31,
    high is a logic 1 and low is a logic 0 (it's inverted by the MAX232) and
    the data goes feet first, so the following 8 bit periods are high, low,
    low,high, high, low, low. Then the input goes high for at least 1 bit

    This all assumes 8N1.

    Paul Burke
  3. Leon Heller

    Leon Heller Guest

    If the RS-232 '1' input is -12V or so, you should get a logic high (+5V) out
    of the MAX232.

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