Using the serial port with a matlab gui  (Page 4/6)

Using matlab to access the serial port (pc)

MATLAB can be used to access the data coming from the serial port. This guide will show the set-up procedures neccesary. Other serial-port readers should also work as long as they are set upwith the parameters specified in the introduction.

Sending data

Before accessing the serial port, it must be initialized through MATLAB. This is done with this code: % Set serial port mode !mode com2:38400,n,8,1 which sets the port to all of neccesary parameters. The port is still not open for writing, however it is now in the correct mode. To open the port, the fopen command is used, which returnsa file descriptor to the port: % open com port for data transfer fid = fopen('com2:','w'); 'com2:' is the port on the PC, 'w' means that we are opening the port for writing, and fid is the file descriptor. For our purposes, you can think of the file descriptor as the portbuffer itself, and when you write to it, you are writing directly to the buffer. To write to the serial port buffer, the fwrite command is used: fwrite(fid,data,'int8'); data is the data to send to the port, fid is the file descriptor of the open port, and 'int8' is the type of data being sent. For a list of different data types, check MATLAB help files with help serial . Since the DSP is blind to the different types and we can only use 8 bits at a time, int8 should work.

Before finishing a function, or before executing a read from the serial port, the port MUST BE CLOSED. Failure to close the port, will result in blocking access to other functions and apps onthe machine that need to use the port. A reset pulse is sent before closing. The port is closed with the fclose command: % send reset pulse fwrite(fid,255,'int8');% close com port connection fclose(fid); It seems intuitive that to read from the port, it need to be opened with a 'r' or a 'r+' instead of 'w'. According to the MATLAB help files this is true, but in practice it does not work. See the nextsection for information on how to read from the serial port. Another method of opening the port is using the fid = serial('com2'); command. This does not seem to work for reading either. See the MATLAB help for more details and methods.

Receiving data

Although MATLAB is supposed to support both writing and reading data from the serial port, reading data seems to either produce no result, generate an error, or crash MATLAB. To remedy the situationGetSerialData() has been written. This function will allow you to get vectors of data from the serial port buffer.

Setting up getserialdata.cpp

You can download a copy of GetSerialdata.dll and skip this step. If you wish to modify the code for GetSerialData.cpp to handle other serial port protocols (such as handshakingand other features) you can use this to help you re-make the code.