Modbus Protocol Question & Answers May 3, 2022 By WatElectronics This article lists 50 Modbus Protocol MCQs for engineering students. All the Modbus Protocol Questions & Answers given below include a hint and a link wherever possible to the relevant topic. This is helpful for users who are preparing for their exams, interviews, or professionals who would like to brush up on the fundamentals of Modbus Protocol. Modbus protocol is a message exchanging protocol that involves reply or request operations. Due to extreme popularity in multiple domains Modbus communication has its functional codes, implementations, and applications. Modbus communication protocol is mainly designed for information transfer between electronic devices using serial lines or through Ethernet connections. It is also labeled as Master and slave types protocol. During this operation, the slaves are kept on hold until a request is sent from the master. This communication is possible with the help of an RTU (Remote terminal unit) that creates data exchange between various devices. Where the master has to initiate a request and the slave has to perform the action and initiate a response, as soon as the response is granted it is received by the Master. Each function code is coded as 8-bit as each byte. These function codes are valid if it ranges between 1-25 and the rest of them 128-255 are set aside for exceptional cases. Functional codes notify the server to perform requested action when there exists a request message from master to slave. Variants of the Modbus protocol are Modbus RTU, Modbus ASCII, Modbus TCP/IP, Modbus plus. Applications of Modbus protocol are in the Medical domain, Home automation, Industries, etc. 1). Which of the following is the alternative name of Modbus protocol ____________. Data transfer protocol Data Communication Protocol Data retrieving protocol None of the above Hint 2). Modbus communication protocol was developed in_____year. 1970 1975 1980 1979 Hint 3). Modbus is a _______ type of communication protocol. Parallel Serial Hybrid None of the above Hint 4). Modbus is used along with_______. PLCs PLDs PALs FPGAs Hint 5). Modbus provides Client/Server or Master/Slaves communication between______ and ______. Optical devices, Buses or Wires. Electronic devices, Networks or Buses. Magnetic devices, Networks or Buses Electromagnetic devices, Buses or Wires Hint 6). Which of the following are the variants of Modbus? DP, TCP RTU, TCP/IP FM, PA PA, RTU Hint 7). Modbus protocol works as _________type protocol. Request/reply Reject/Accept Retake/Reply None of the above Hint 8). Modbus protocol contains ____master and _______ slaves. Multiple, Single Single, Multiple Single, single Multiple, multiple Hint 9). Identify the data rate for Modbus is ______. 50 Hz 200 Hz Not specified 150 kHz Hint 10). Network of Communication protocol is formed by one master and ___ slaves with a unique address. 230 298 247 300 Hint 11). PAC stands for___________. Programmable Array Component Programmable Automation component Programmable automation controller Programmable Automation client Hint 12). HMI is a________ client. Human machine Interface High machine interface Human Manufacturing interface None of the above Hint 13). Which of the following are the Modbus applications _________. Healthcare Transportation Home automation All of the above Hint Modbus Protocol Quiz Questions and Answers. 14). How many types of Modbus Function codes exists? 2 5 8 10 Hint 15). The first Modbus function code contains _____type of register. Read discrete input Read holding registers Read coil Write single coil Hint 16). The second Modbus function code contains _____type of register. Read discrete input Read holding registers Read coil Write single coil Hint 17). The third Modbus function code contains ______type of register. Read discrete input Read holding registers Read coil Write single coil Hint 18). The fourth Modbus function code contains ______type of register. Read discrete input Read input registers Read coil Write single coil Hint 19). The fifth Modbus function code contains ______type of register. Read discrete input Read input registers Read coil Write single coil Hint 20). Write single holding register exists with _____Modbus function code. 3 5 6 7 Hint 21). The fifteenth Modbus function code holds ______type of register. Read discrete input Read input registers Read coil Write multiple coils Hint 22). The sixteenth Modbus function code holds ______type of register. Read discrete input Write multiple holding registers Read coil Write multiple coils Hint 23). Which of the following are extensions of Modbus protocol? 16 bit slave address 32 bit data size Word swapped data All of the above Hint 24). ____ is assigned while transferring data via to Modbus Address Bus Information Registers Hint 25). ADU stands for _______________. Application Data Unit Address Data Unit Application Direct Unit Address Direct unit Hint 26). Modbus _____frame format used on a asynchronous serial data lines like RS-485/EIA-485. ASCII RTU TCP/IP UDP Hint 27). Modbus represented in ______frame format? ASCII RTU TCP/IP UDP Hint 28). Modbus ______frame format primarily used on Ethernet networks. ASCII RTU TCP/IP UDP Hint Modbus Protocol MCQs for Exams 29). Generally, Modbus TCP/IP capable devices usually avoids ________. Unit identifier Protocol identifier Transaction identifier Data bytes Hint 30). How many types of File record access exists in Modbus function codes? 1 2 3 4 Hint 31). For Function code 5 (write single coil) has value to force/write: 0 for OFF and 65,280 for ON 1 for OFF and 62,580 for ON 0 for OFF and 62,580 for ON None of the above Hint 32). In Modbus data model composed of ______blocks. 2 4 6 8 Hint 33). Each element within a data block of Modbus data model is obtained from____. 1 to FFFF 1 to 65,535 1 to n None of the above Hint 34). _______ numbers span from 000001 to 065536. Discrete Input Register Coil Input Register Holding Register Hint 35). _______ numbers span from 100001 to 165536. Discrete Input Coil Input Register Holding register Hint 36). _______ numbers span from 300001 to 365536. Discrete Input Coil Input Register Holding register Hint 37). _______ numbers span from 400001 to 465536. Discrete Input Coil Input Register Holding Register Hint 38). Modbus Plus involves________ operation. Address Coincide Token Passing Mixed Data Types Floating Types Hint Modbus Protocol Interview Questions and Answers 39). In function code-16 address of first holding register to write must be_______ value. 8-bit 16-bit 32-bit 64-bit Hint 40). In function code-16 , there exists of ______number of bytes of register values. 8-bit 16-bit 32-bit 64-bit Hint 41). Maximum length of Modbus PDU is_____. 234 250 253 235 Hint 42). Maximum length of Modbus APU is ___on RS485. 256 265 245 254 Hint 43). How many registers can be written once in function code 16? 125 215 123 213 Hint 44). In function code 4, how many registers are requested at once for RTU? 125 215 123 213 Hint 45). In function code 4, how many registers are requested at once for TCP? 125 215 123 213 Hint 46). Each value of discrete input is denoted by_____. Binary Hexadecimal Octal Zero Hint 47). In function code 1, the discrete inputs has ___input values per byte. 8 7 6 5 Hint 48). Which of the following are the other kinds of Modbus protocol versions: Enron Pemux Modbus over UDP All of the above Hint 49). PLCs acts as Modbus ______ version. Servers Transmitters Receivers Buses Hint 50). Modbus RTU supports upto ____ devices. 28 32 64 72 Hint Please fill in the comment box below. Time is Up! Time's up
