MATLAB: Am I not able to communicate with an instrument connected over Serial/RS-232 using FPRINTF in MATLAB

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I am trying to communicate with an instrument connected over a Serial (RS-232) connection on my PC. I have tried doing this with HyperTerminal and MATLAB.

The interaction with the device using HyperTerminal has been working fine. I am able to send commands and get responses back both by manually typing the commands at the terminal, and by using the “Send text file” feature, with a text file containing pertinent commands.

However, when I try to communicate with the device through MATLAB by using the FPRINTF command, I receive the issued command back; i.e., the issued command is echoed back to MATLAB after using the FSCANF command. I observe the same behavior when trying more low-level routines, such as FWRITE to send commands, and FREAD to receive the instrument's replies.

Best Answer

1) Typically, while typing in the data from the HyperTerminal, it is observed that along with the data, a Carriage Return gets appended to the message in addition to a Line Feed (if using the "Send line ends with line feeds" feature in ASCII Setup). Using Serial Port monitoring software, one can observe that the transmitted data from HyperTerminal has 'OD' and 'OA' appended to it, which represent Carriage Return and Line Feed, respectively.

2) However, when you are trying to write data from MATLAB, the data has just the Line Feed appended to it by default. Hence, in order to include the Carriage Return as well, set the Terminator property to a new value as shown in the following example:

set(obj,'Terminator','CR/LF')

3) The echoing process while sending data from MATLAB could also be occurring due to the device being in an error state. Verify if this is true by consulting the device documentation.

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baudrate 115200, flowcontrol hardware, BytesAvailableFcnMode terminator, terminator LF

MATLAB: Unexpected Results When Interacting with the ATI Axia80-M20 using the Serial Interface

The instrument's serial communication interface was mainly intended for terminal device applications, where commands (and end-of-line characters) are manually typed one letter at a time, whereas MATLAB serial write functions send all characters in quick succession. A custom fuction writing one character at a time with a pause between characters is needed.

The instrument manual describes only the terminal device communication workflow using PuTTY.

https://www.ati-ia.com/app_content/Documents/9610-05-Serial%20Axia.pdf

Below are some properties of this particular device that we have observed:

The instrument takes "CR/LF" for read terminator and "CR" for write, instead of "LF".
The instrument cannot take multiple characters at once, it requires pauses between characters.
The instrument echoes back the command characters received.
The instrument does not appear to have consistent behavior, for the same command, sometimes it works, sometimes it returns "command not found"
The output is spread over multiple lines, so you have to do fscanf several times to get the whole output.

From the properties above, the intended use of serial communication of this device is for terminal interaction, where commands and line terminators are typed in one letter at a time.

To correctly use this device, please first connect to the device using the "serial" object as below:

FT = serial('COM18','BaudRate',115200);
FT.Terminator = {'CR/LF','CR'};
fopen(FT)

Then define a function that takes a command string as argument and sends one character at a time to the device.

Since we are sending one character at a time, we use fwrite instead of fprintf.

function writeCommand(obj, cmd)
    for i = 1:numel(cmd)
        fwrite(obj, cmd(i))
        pause(0.25)
    end
    fwrite(obj, 13)
end

Then use the function defined above to send command to the device and read with fscanf. Note that as mentioned above, the output might spread over multiple lines, so you have to scanf multiple times to read the whole output:

% command to get into "Robot Mode"
% According to section 6.1 on the manual in the link below, first you want to
% make sure you enter "Robot Mode" with instrument command "m" before collecting
% data with instrument command "r".
writeCommand(FT, 'm')
pause(0.5)
% read whole output, you can also define this as a function
while (FT.BytesAvailable > 0)
    fscanf(FT)
end
% command for reading data
writeCommand(FT, 'r')
pause(0.5)
while (FT.BytesAvailable) > 0
    fscanf(FT)
end
% you can also send other commands that are mentioned in the manual
% writeCommand(FT, 'h')

Close the connection after use:

fclose(FT)
delete(FT)

Best Answer

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