Modbus Kya Hai? Ek Complete Guide (History, Structure, aur Function Codes)

Published: February 27, 2026 ⏳ Calculating...

Industrial Automation ki duniya mein agar koi aisi language hai jo lagbhag har device samajhta hai, toh wo hai Modbus. Chahe aap kisi PLC ko VFD se connect kar rahe hon, ya kisi smart transmitter ka data SCADA par le ja rahe hon, Modbus har jagah maujood hai. Is post mein hum Modbus ki history, iske modes, addressing, aur function codes ko detail mein samjhenge.

💡 Pro Tip: Agar aap automation technician hain, toh Modbus ko deeply samajhna aapke career ke liye sabse bada plus point ho sakta hai.

Modbus Protocol Ki History

Kuch communication standards isliye hit nahi hote kyunki unhe koi badi company push karti hai, balki wo isliye hit hote hain kyunki wo simple aur use karne mein aasan hote hain. Modbus bhi unhi mein se ek hai.

Modbus ki shuruaat 1979 mein hui thi, jab PLC banane wali company Modicon (jo ab Schneider Electric ka hissa hai) ne ise launch kiya tha. Iska main maqsad PLCs aur dusre devices ke beech data exchange karna tha. Ye ek Master/Slave (Client/Server) architecture par based open standard tha.

ℹ️ Info: Shuru mein Modbus RS-232 par chalta tha, lekin baad mein RS-485 ka use hone laga kyunki isse lambi distance aur multi-drop network banana aasan ho gaya tha. Aaj ke time mein ye TCP/IP (Ethernet) par bhi chalta hai!

Modbus Kaise Kaam Karta Hai? (Master/Slave System)

Modbus controllers Master/Slave method ka use karte hain. Iska seedha sa matlab hai ki network par sirf ek device (Master) baat shuru kar sakta hai. Baki sabhi devices (Slaves) sirf master ki baat sunte hain aur uske command ka jawab dete hain.

Master kisi ek specific slave se bhi baat kar sakta hai, ya fir sabhi slaves ko ek sath command (broadcast message) bhej sakta hai.

Har Modbus message frame ka structure kuch aisa hota hai:

Device Address: Kis slave se baat karni hai.
Function Code: Slave ko kya karna hai (Read ya Write).
8-bit Data Bytes: Asli data ya value.
Error Checking: Message raste mein kharab toh nahi hua, ye check karne ke liye.

Modbus Serial Transmission Modes: ASCII aur RTU

Serial Modbus connection mein do main transmission modes hote hain: ASCII aur RTU. Network par sabhi devices ka mode same hona zaroori hai.

1. Modbus ASCII Mode

Is mode mein messages readable ASCII format mein hote hain. Iska fayda ye hai ki characters ke beech 1 second tak ka gap ho toh bhi error nahi aata, isliye ye slow communication ke liye achha hai. Isme error checking ke liye LRC (Longitudinal Redundancy Check) ka use hota hai.

Start(:) + Address(2 chars) + Function(2 chars) + Data(x chars) + LRC(2 chars) + End(CR/LF)

2. Modbus RTU Mode (Sabse Popular)

RTU (Remote Terminal Unit) mode mein data binary format mein bheja jata hai. Ye ASCII se fast hota hai kyunki isme data compact hota hai. Isme error checking ke liye CRC (Cyclic Redundancy Check) ka use hota hai. Dhyan rahe, isme message ek continuous stream ki tarah jana chahiye, beech mein lamba gap nahi ho sakta.

Start(3.5 char delay) + Address(8 bits) + Function(8 bits) + Data(n x 8 bits) + CRC(16 bits) + End(3.5 char delay)

⚠️ Warning: ASCII aur RTU devices ek hi network par aapas mein baat nahi kar sakte. Unki bhasha alag hoti hai!

Modbus Addressing System

Modbus network mein har slave ka ek address hota hai, jo 1 se lekar 247 tak ho sakta hai. Address 0 ko "Broadcast" ke liye reserve rakha gaya hai (yani address 0 par bheja gaya command sabhi slaves ko manna padega).

Lekin jab hum kisi slave ke andar ka data padhte hain, toh mamla thoda alag hota hai. Devices ke andar holding registers ya coils ka address 1 se 10000 tak hota hai, lekin Modbus message mein address 0 se 9999 ke beech bheja jata hai. Yani agar aapko Output 18 read karna hai, toh aapko message mein Address 17 bhejna hoga (-1 offset).

Modbus Function Codes (Sabse Zaroori Hissa)

Function code slave ko batata hai ki use aakhir karna kya hai. Valid function codes 1 se 255 tak hote hain, par industrial line mein kuch hi codes sabse zyada use hote hain:

Function 01 (Read Coil Status): Ye kisi discrete output (jaise relay ya motor ON/OFF status) ko read karne ke kaam aata hai.
Function 02 (Read Input Status): Ye discrete inputs (jaise sensor ya switch) ka status read karta hai.
Function 03 (Read Holding Registers): Ye kisi device ke internal 16-bit parameters (jaise Temperature, Speed, ya Pressure ki analog value) ko read karne ke kaam aata hai.

💡 Note: Agar slave koi command perform nahi kar pata ya koi error aata hai, toh wo reply mein function code ka "highest bit" ON karke bhejta hai. Isse master ko pata chal jata hai ki command fail ho gaya hai.

Modbus Protocol Ke Alag-Alag Versions

Time ke sath Modbus ne khud ko upgrade kiya hai. Aaj ke time mein iske kayi variants market mein hain:

Modbus RTU: Serial communication ke liye sabse common. Binary data aur CRC ka use karta hai.
Modbus ASCII: Serial par chalta hai, readable ASCII characters aur LRC ka use karta hai.
Modbus TCP/IP: Ethernet network ke liye design kiya gaya hai (Port 502). Isme alag se checksum ki zaroorat nahi hoti kyunki TCP layer khud error check kar leti hai.
Modbus Plus (MB+): Ye Schneider Electric ka thoda advance aur fast network hai jo peer-to-peer communication support karta hai (yani koi bhi device dusre device se baat start kar sakti hai).
Enron Modbus: Ye specially oil & gas industry ke liye banaya gaya tha, jo 32-bit floating-point variables aur historical data ko support karta hai.

Industrial Automation field mein aage badhne ke liye Modbus ko deeply samajhna bohot zaroori hai. Ye protocol bhale hi purana ho gaya hai, par iski simplicity isey aaj bhi automation ka "King" banaye hue hai.

Agar aapke paas Modbus se juda koi sawal hai, toh niche comment zaroor karein!