If you check
help icinterface.fwrite
you will see that by default it converts the input data to uchar. I noticed it by running echotcpip, as the returned data was truncated. Checking with a simple python echo script I confirmed that. After changing
fwrite(tcpip_pipe,message)
to
fwrite(tcpip_pipe,message,'int16')
I managed to communicate to modtools' "Modbus Slave" application on windows. This is the code I got working:
% configuration of TCP/IP channel
IPADDR='127.0.0.1';
PORT=10502; % The port should be 502, but this is previleged under linux
tcpip_pipe=tcpip(IPADDR, PORT); %IP and Port of ATV32
set(tcpip_pipe, 'InputBufferSize', 512);
tcpip_pipe.ByteOrder='bigEndian';
try
if ~strcmp(tcpip_pipe.Status,'open')
fopen(tcpip_pipe);
end
disp('TCP/IP Open');
catch err
disp('Error: Can''t open TCP/IP');
end
transID=uint16(0);
apparently, the channel is successfully opened.
transID = uint16(transID+1); % 16b Transaction Identifier
ProtID = uint16(0); % 16b Protocol ID (0 for ModBus)
Lenghf = uint16(6); % 16b Remaining bits (6)
UnitID = uint16(1); % Unit ID (0)
UnitID = bitshift(UnitID,8);
FunCod = uint16(6); % Function code: write (6)
UnitIDFunCod = bitor(FunCod,UnitID);
% Concatenation of UnitID & FunctionCode
% in one uint16 word
% According to modbus protocol, UnitID and Function code are 8bit data.
% In order to maintain the same data tipe in vector "message", I converted
% each of them to uint16, and used "bitor" to create a uint16 word when
% the MSB is the UnitID and the LSB is the function code
Add = uint16(03); % 16b Adress of the resister (8501)
Val = uint16(transID*10); % 16b Data (5)
message = [transID; ProtID; Lenghf; UnitIDFunCod; Add; Val];
disp(message);
fwrite(tcpip_pipe, message,'int16');
while ~tcpip_pipe.BytesAvailable,end
tcpip_pipe.BytesAvailable
res=fread(tcpip_pipe,tcpip_pipe.BytesAvailable)
fclose(tcpip_pipe);
