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Original question:

UART High baud rates

MAX3232: What baud rate to use with this chip?

RuggedEngie
Intellectual 375 points

Part Number: MAX3232

I know baud does not equal bps but I am unsure what to configure my PC COM port for use with this chip?

Is 9600 baud okay for RS232 serial port? I see the MAX3232 minimum data rate is 150 kbit/s but that is not the same as baud right?

  • 0
    TI__Guru 62920 points

    Hello,

    You would set the PC COM port's baud rate to something that is supported by the target device (whether it be a printer, modem, whatever).  As long as it is lower than the maximum signaling rate that is specified by transceiver you will be OK (i.e., so that the transceiver does not become a bottleneck).  Keep in mind that the PC isn't communicating "to" the MAX3232 so much as it is communicating "through" it to some other device.  Let me know if that doesn't make sense to you.

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    Intellectual 375 points

    Hi Max,

    That does make sense. In this case we have a PC talking to a PC. One PC is using the MAX3232. It is not currently working though. I thought maybe it was the COM port setting but maybe this has to do with using or not using a null modem cable? Or something else?

  • 0 in reply to Miguel Robertson
    Intellectual 375 points

    Also, the MAX3232 datasheet mentions its' minimum data rate is 150kbit/s? Does this not really matter?

  • 0 in reply to RuggedEngie
    TI__Guru 62920 points

    The 150 kbps is not a minimum (the device would work for arbitrarily low data rates without a minimum restriction).  I actually thought that spec was a little strange since it seems to suggest the maximum rate achievable may be 150 kbps in some instances whereas I've always regarded this as a 250 kbps part.  I've noted that to look a little further into.  For your case, though, it sounds like you are targeting <150 kbps anyway so no immediate cause for concern there.

    I'd definitely look into the cabling issue you mentioned.  If you are connecting a PC to a PC, they should have the same pin assignments on either end of the cable.  Without a null modem cable or adapter, then, you would be connecting both sides' transmitters together and both sides' receivers together.  That's not how it should work - transmitters should connect to receivers.

    Max

  • 0 in reply to Miguel Robertson
    Intellectual 375 points

    Thanks Max! Very informative!