Serial port communication

I have an On-Board Diagnostics (OBDII) tool that I am trying to read the values from. This tool helps me trouble codes on a car's ECU. I can use hyperterminal to read the values through the USB. When I open the terminal with COM1, baud rate of 9600 and type in 03, it returns me some value.

How do I do the same in MATLAB? Is this it or do I need to do more?

s = serial('COM1'); fopen(s) fprintf(s,'03') out = fscanf(s)

Please suggest.

Answer 1

[Krishna Gummadi]

I had to add this before fscanf to work:

fprintf(s,'%s','13'); %CR

[Walter Roberson]

'13' would not send a CR, but 13 not in quotes would. That would be the same, though, as coding \r in the format like I suggested.

Answer 2

[Walter Roberson]

What terminator does the remote system need? fprintf(s,'03') is defined as fprintf(s,'%s\n','03') which sends 03 followed by whatever terminator is configured for the port. If that terminator does not match what the remote system is expecting, you could have difficulty.

Answer 3

[Krishna Gummadi]

The document indicates this:

"All messages to the OBD Prompt must be terminated with a carriage return character (hex ‘0D’) before it will be acted upon. If a command has been started but not terminated by a ‘0D’ it will be aborted after 20 seconds of inactivity"

So, should I say fprintf(s,'030D') instead?

[Walter Roberson]

You could set the terminator to carriage return, or you could use

fprintf(s,'%s\r', '03')