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Trying to get a program to work with a serial port, but there is no serial port configuration settings given.

I have an old hardware board (a Stanley MC521 Controller) from late 1990s I guess. It has a serial port and I am trying to find out the baud rate and parity settings. How to identify the correct baud rate of an unknown serial port?

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    \$\begingroup\$ Try all the common ones until you get sensible looking data out of it? \$\endgroup\$
    – Nick Johnson
    Commented Jun 30, 2015 at 14:15
  • \$\begingroup\$ Maybe tell us what the device is (manufacturer and model?) Some one might recognize it or be able to find a handbook online. \$\endgroup\$
    – JRE
    Commented Jun 30, 2015 at 14:15
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    \$\begingroup\$ Start with 96008n1 \$\endgroup\$
    – JRE
    Commented Jun 30, 2015 at 14:19
  • \$\begingroup\$ "I have a something I don't know what it is. How can I know what it is?" Is it looking like a good question to you? \$\endgroup\$
    – Eugene Sh.
    Commented Jun 30, 2015 at 14:25
  • \$\begingroup\$ Stanley MC521 Controller \$\endgroup\$
    – needoriginalname
    Commented Jun 30, 2015 at 14:40

2 Answers 2

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The most direct way is to look at the signal on an oscilloscope, assuming the device is emitting a signal to begin with. (Bonus: This will also help determine the correct pinout of the connector.)

You can easily determine the bit period (1 / the baud rate), the word length and how many stop bits are being used.

Determining the parity setting requires a bit more work, and it might be easier to just try the different parity settings once you have the other parameters set correctly.

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  • \$\begingroup\$ Or you have one of these scopes that can autodetect the parameters in a lot of cases. \$\endgroup\$
    – PlasmaHH
    Commented Jun 30, 2015 at 15:07
  • \$\begingroup\$ I do not have an oscilloscope at my disposal. Just a multimeter. \$\endgroup\$
    – needoriginalname
    Commented Jun 30, 2015 at 17:21
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Attempting to answer and consolidate a few inputs from comments: Many ways:

I prefer to check the waveform of transmit signal on oscilloscope.

Second is to start from the Typical baud rates from lower to higher values

Third, all standard values skipping the typical values.

Assuming the hardware is sending out something with out a query from the computer. In the later case, it might be impossible.

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