Making RS-232 Triggers Work

RS-232 can sometimes be a bit tricky to get up and running, especially for someone using it for the first time. There are a few things to check that are the usual culprits:

  1. Go to the serial device properties in the device manger.
  2. Check that the Serial port selected is correct.
  3. Check that the Bit rate, Data Bits, Parity, and Stop bits are the same. The defaults in the programmer do not usually work here. You will be able to find the values either in the manual for the device you are connecting to, or in the setup options of the device.
  4. Make sure you are sending 2 values plus a carriage return (ASCII 13) from the external device. The programmer does not read a command until a carriage return is sent. This is by far the most common problem encountered when setting up a serial link to the programmer.
  5. Make sure that you are not confusing ASCII value types. This can be a bit confusing if you are trying to use numbers. The ASCII code is a mapping of the number 0-255 to characters. The ASCII value 1 does not match the character ‘1’, so if you try to mix and match, you will end up with missing triggers. Also, these characters are case sensitive, so ‘A’ is not the same thing as ‘a’. If you send the command “A1<CR>” from your external hardware, you will want the trigger to read:
  • Value A: 65=’A’
  • Value B: 49=’1′

You can find more information about ASCII here:

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