104/11/2023

Development of a Modbus RTU to Modbus TCP/IP compiler on Netburner platform

Prepared by: Pratik Vyas

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Introduction

• An open source protocol – Modicon Inc.• Dick Morley Innovator• For Industrial Automation System• Communicate over Master – Slave Technique• Remotely access Machineries• Less human effort require• Modbus TCP/IP• Modbus RTU

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Modbus TCP/IP Stack

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Modbus TCP/IP Stack

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• Creation of socket()• int sockid= socket(family, type, protocol);

• sockid: socket descriptor• family: integer, communication domain, PF_INET• type: communication type like SOCK_STREAM &

SOCK_DGRAM • protocol: specifies protocol, IPPROTO_TCP:: Indicates

that the TCP protocol is to be used

• socket call does not specify where data will be coming from, nor where it will be going to –it just creates the interface!

Socket

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Modbus TCP/IP Stack

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• reserves a port for use by the socket• int status = bind(sockid, &addrport, size);

• sockid: integer ID• addrport: the (IP) address and port of the machine

for TCP/IP server, internet address is usually set to INADDR_ANY, i.e., chooses any incoming interface

• size: the size (in bytes) of the addrport • status: upon failure -1 is returned

Bind

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int sockid;struct sockaddr_in addrport;sockid= socket(PF_INET, SOCK_STREAM, 0);

addrport.sin_family= AF_INET;addrport.sin_port= htons(5100);addrport.sin_addr.s_addr = htonl(INADDR_ANY);

if(bind(sockid, (struct sockaddr *) &addrport, sizeof(addrport))!= -1) {

…}

Bind

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• bind can be skipped • Stream socket: The OS finds a port each time the socket sends a

packet

Bind

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Modbus TCP/IP Stack

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• Instructs TCP protocol to listen for connections• int status = listen(sockid, queueLimit);

• sockid:: integer, socket descriptor• queuelen:: integer, # of active participants that can “wait” for a

connection• status:: 0 if listening, -1 if error

• The listening socket is used by the server only as a way to get new sockets

Listen

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Modbus TCP/IP Stack

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• The client establishes a connection with the server by calling connect()

• int status = connect(sockid, &foreignAddr, addrlen);– sockid:: integer, socket to be used in connection– foreignAddr:: address of the participant– addrlen:: integer, sizeof(name)

• connect() is blocking

Connect

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• The server gets a socket for an incoming client connection by calling accept()

• int s = accept(sockid, &clientAddr, &addrLen);– s:: integer, the new socket (used for data-transfer)– sockid:: integer– clientAddr:: address of the active participant– addrLen:: sizeof(clientAddr)

• accept() waits for connection before returning

Accept

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Modbus TCP/IP Stack

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• int count = send(sockid, msg, msgLen, flags);– msg:: message to be transmitted– msgLen:: length of message (in bytes) to transmit– flags:: special options, usually just 0

• int count = recv(sockid, recvBuf, bufLen, flags);– recvBuf:: stores received bytes– bufLen:: bytes received– flags:: special options, usually just 0

• Calls are returns only after data is sent / received

Exchanging Data

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Close

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• When finished using a socket, the socket should be closed• status= close(sockid);

– sockid:: socket being closed– status:: 0 if successful, -1 if error

• Closing a socket closes a connection

Close

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User Interface

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Further Implementation

• After getting data from the client forward it on Modbus RTU stack and RTU stack will send it to device.

• In reverse device will send information will get to the Modbus RTU stack and it will return to back on Modbus TCP/IP stack.

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Thank you