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Questions tagged [modbus]

Modbus is a serial communications protocol commonly used by PLCs (programmable logic controllers) and other industrial control systems. While originally based on traditional serial communication, many extensions exist to allow communication over other networks such as TCP/IP.

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rs485/modbus issue

I am trying to enable modbus RTU communication between 2 inverters. Both are set up with unique IDs, 9600Hz, 1 stop bit, No parity bit. I can communicate with 1 at a time, as shown below in the ...
fruit salad's user avatar
0 votes
2 answers
115 views

Why are there two wires connected to each terminal of the RS485 port in energy meters

I want to connect the energy meters of our clients to a gateway so that the gateway can communicate with the meters using Modbus. I have visited several electrical rooms that have gateways installed ...
Somanna's user avatar
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12 views

Issue with MAX3140 UART when sending 64-bit frame using 16-bit frame configuration

I am facing an issue with the MAX3140 UART when attempting to send a 64-bit frame through a 16-bit frame configuration. The MAX3140 uses a 16-bit frame for communication, where the upper 8 bits are ...
Noushad's user avatar
2 votes
2 answers
256 views

Is Modbus suitable for motion control positioning?

I need to issue position setpoint commands to a servo drive 50 times/sec. The drive will be responsible for closing the PID loop, etc, while the motion controller I'm developing will handle generating ...
19172281's user avatar
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1 answer
35 views

Can TCC-100/100I Series Industrial RS-232 to RS-422/485 converters with optional 2 kV isolation convert RS485 to RS232? [closed]

I want to convert RS485 to RS232 to connect it to a Moxa Nport 5610 - 16 port RS-232 Ethernet serial device server. Can I use a TCC-100/100I Series Industrial RS-232 to RS-422/485 converter to convert ...
suraj s kumar's user avatar
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1 answer
47 views

Pulling Receiver Enable Low for RS-485 Transceiver is being transmitted as a byte in Modbus packet

I am running into an issue where pulling RE low on my Max3441EESA is appearing as an extra byte in my Modbus message. I am currently testing the Modbus capability of my PIC32 MCU with a Modbus slave ...
SubjectFocused's user avatar
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1 answer
76 views

modbus control of BLD-300R brushless DC motor controller [closed]

I have a BLD-300R generic brushless motor driver, purchased from a chinese webstore. It has a RS485 port for modbus control from a PLC, but I cannot find the protcol specs (baud rate, stop bits, ...
Michael Ward's user avatar
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121 views

Potential Reasons for Fault on RS-485 Transceiver

I am working with the MAX3441 RS-485 transceiver, but I have run into faults with the three transceivers I have tested, so I am wondering if anyone can shed some insight on potential reasons for the ...
SubjectFocused's user avatar
2 votes
2 answers
190 views

Can I connect ten RS485 modbus kWh meters to one RJ45 modbus server? [closed]

If I have a fusebox with about ten/fifteen eastron sdm630 and Orno OR-WE-515 kWh meters with RS485 modbus, can I daisy chain ...
Tim's user avatar
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3 votes
2 answers
123 views

Hardware advice for communicating data between two different MODBUS protocols using RS-485

I am trying to build a small device that will act as translator between two devices having two different RS-485 MODBUS protocols. This device will store 4 different values from "Device 1" ...
Niks's user avatar
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1 answer
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How to debug modbus rtu address space problems? [closed]

I have an "Ewon Flexy server" and an "IMO SD1 Inverter" connected via Modbus RTU RS485. I can change some of the parameters with Flexy interface and observe the change in the ...
Juha's user avatar
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1 answer
251 views

Can USB-to-SERIAL dongle be used to drive an RS-485 transceiver?

Pictured below is a simple arrangement used to read the Temperature sensor from the PC. Standard/Protocol is MODBUS RTU RS-485 Half-Duplex. I've used this arrangement with both modpoll.exe and ...
Noideas's user avatar
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0 answers
129 views

Modbus receiving same message as sent

I am having a problem when communicating with a Modbus slave. I have made a circuit with the translator shown in the picture. UART2_RXD and ...
magn4258's user avatar
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1 answer
122 views

Modbus ASCII messages delimiter

I need to implement Modbus messages reception over UART. For RTU it's easy because UART on my uC has configurable idle receive line detection. However, for ASCII the task is tricky - the delimiter is ...
asiemasz's user avatar
1 vote
1 answer
276 views

MODBUS TCP Read response query - second opinion required

I am having an interoperability problem between a Modbus/TCP driver from one company and a Modbus/TCP device from another. The Modbus driver I am using seems to be able to correctly read all but four ...
dwp321's user avatar
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0 answers
350 views

Modbus RTU on ESP8266 to control VFD

Hoping to get some help on setting up a NodeMCU (esp8266) with this 1 arduino library to control a Variable Frequency Drive (VFD). I'm afraid to say that I almost need help from square one, as I'm ...
Christian Carlsson's user avatar
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1 answer
328 views

Communicating with 6 TTL devices that support the Modbus protocol

I am working on project using Hukseflux SR05-D2A2 thermal sensors. These sensors support Modbus communication through a TTL interface. The objective is to read the value at a specific address in the ...
RandomEye's user avatar
2 votes
1 answer
1k views

Modbus TCP illegal packet (CRC) time-out problem in gateway

I am connecting a Modbus gateway to an RTU acquisition system. I am using a MOXA Gateway MB3480 with a RS485 (2 wires) connector. The thing is that I can't read the data all the time; I receive a time-...
Developing Electronics's user avatar
0 votes
2 answers
658 views

How to read MOXA gate Modbus RTU to Modbus TCP in Python?

I have got some MOXA devices. One of them is an Mgate MB3180. I want to code in a program in Python to read the data using TCP. I don't know if I have to use a regular "TCP reading" or an &...
Developing Electronics's user avatar
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0 answers
114 views

Same holding register address for different purposes in Modbus?

I have a device which is supposed to support the Modbus protocol. By Function-3, I can read an input status at address-1000, but the same address-1000 is used as an output so I can write the value to ...
mehmetfa's user avatar
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4 votes
4 answers
2k views

Can I test if a MODBUS server device is active?

We have a device which has a RS485 Modbus connection. This device supposedly acts as a server on the bus. We are in a position where it is not clear if the Modbus feature is even turned on or active. ...
James Mason's user avatar
1 vote
1 answer
223 views

Modbus gateway and VCOM configuration using Linux

I am connecting a Modbus Gateway (USER-TCP232) to a Linux PC. The thing is that it does not use MODBUS TCP, it just packs the RTU data frame over TCP, so I cannot use MODBUS TCP in the PC, I must use ...
Developing Electronics's user avatar
0 votes
1 answer
141 views

Project setup help: Siemens S7-1200 with Modbus and OPC UA

I'm currently planning a PLC project but I'm not sure how to put the components together. About my setup: I want to integrate a Siemens S7-1200 as master PLC. The PLC should control a subordinate ...
Florian's user avatar
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2 answers
102 views

VFD speed reference command: Will MODBUS/TCP have better resolution than 4.0 ~ 20.0 mA

I need help to understand the difference between tranditional 4.0~20.0 mA and digital communication (for example MODBUS/TCP) Assume: a PLC communicates with a VFD to control a variable speed pump from ...
RXS's user avatar
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1 vote
3 answers
317 views

Microcontroller requirements for multiple Modbus controllers

I am in the process of trying to design a circuit that will have four RS485 RTU Modbus ports, two acting as clients and two acting as servers, on which I will connect up to fifteen sensors. I am ...
Aleš Kramžar's user avatar
1 vote
1 answer
176 views

SIM7080 UART Noise interfacing with PIC18F4550

I'm working on a project where I read data over Modbus line and send it in the cloud service through a SIM7080 CATM modem. I'm using PIC18F4550 as MCU. As that PIC18F has just one UART module, I'm ...
andradecaio's user avatar
1 vote
1 answer
2k views

Modbus over RS485 - no response from device

I am trying to connect to Epever Tracer AN Solar Charge controller from ESP32 using below Max485 module but I can't get any repsonse from device. I was trying to use exactly the same setup mentioned ...
michalo's user avatar
  • 25
0 votes
1 answer
56 views

Is it advisable to make communication re attempts in modbus?

In my system, I know that the approximate response time between master-slave is 10ms, if the slave does not receive communication during those 10ms then it detects an error and the motors turn off. Is ...
Ricardo Casimiro's user avatar
2 votes
2 answers
1k views

Maxim MAX3485ESA+T vs SP3485EN-L/TR

I have a question about the MAX3485ESA+T RS485 Transceiver. I ordered a PCB with a MAX3485ESA+T and the project doesn't work. The previous design was with a SP3485EN-L/TR and it worked well, but I had ...
Eli Saadon's user avatar
0 votes
0 answers
311 views

How to identify Modbus device speed rate?

In particular how to identify it without causing device misbehaving. Either new device is being connected, and master has no idea what baud rate the device is configured with (assume it knows about 8/...
Anonymous's user avatar
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0 votes
1 answer
576 views

RS485 MODBUS ARDUINO: Print multiple response data frame from soil sensor

Hi everyone. I'm guiding myself from tutorial https://how2electronics.com/measure-soil-nutrient-using-arduino-soil-npk-sensor/ I'm using... Hardware components: RS485 Arduino uno Charger 9V (Only for ...
Mike's user avatar
  • 3
1 vote
2 answers
473 views

How to connect a slave device to an RS-485 network without a signal ground reference terminal?

I want to connect a flow meter and a variable frequency drive (VFD) to the same modbus network but the absence of a signal ground reference terminal on the flow meter is causing me some confusion with ...
topheruk29's user avatar
3 votes
4 answers
8k views

Rs485 A & B Labels being used inconsistently

I would like to know if there is an official standard with regards to rs-485 terminals being labelled A & B. I have always believed: A=> + (positive) and B=> - (negative) however, I have ...
Zapnologica's user avatar
3 votes
1 answer
1k views

Can MAX485 TTL-to-RS-485 module be used as UART-to-RS485 module?

I'm trying to make a bridge from Modbus til Home Assistant using an ESP8266 (as outlined here), which uses an UART-to-RS485 module. I have this MAX485 TTL to RS-485 Interface Module. I'm not competent ...
cbh's user avatar
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1 vote
0 answers
1k views

Need Help Connecting Arduino to PC via RS485 with Max485 breakout board

I am currently attempting to connect an arduino to a PC via the RS485 communication protocol using a max485 to convert the RS485 to serial. It does not however appear to be receiving any data at all. ...
Patrick Voorhoeve's user avatar
0 votes
1 answer
180 views

PC to MCU ModBus Communication Problem

Im trying to create a communication between PC to MCU with ModBus, so i used pyserial at PC side and used freemodbus at MCU side. But it did not worked. I tested PC code with Modbus program and its ok,...
U.Sim's user avatar
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0 votes
0 answers
237 views

Want to use SPI sensor in RS485 modbus

I want to use multiple ICM20948 over SPI to RS485 with esp32 . is there anyway to do it and also is there have any other IMU which support rs485?
sakib mozomder's user avatar
0 votes
1 answer
6k views

Modbus Vs CANopen - Which one should I choose?

Modbus Vs CANopen - Which one should I choose if I want: Broadcast to all units Talk to specific units Robust Send lots of data Implement for embedded systems Easy to use Using in new projects with ...
euraad's user avatar
  • 1,324
0 votes
1 answer
359 views

Half duplex connection with a full duplex cevice

I have a sensor that I want to use with Modbus RTU and am not sure if I can use half duplex or if I need to use full duplex. I would also like to get some suggestions how to read from it with my ...
Moritz Pfennig's user avatar
3 votes
3 answers
2k views

Good idea to use UART in half-duplex mode when using RS485 transceiver?

Most 2-wire RS485 implementations I have seen use both UART RX and TX pins which works of course. And I have done so. But I was wondering whether using UART in half-duplex mode is a good alternative ...
JeromeBu1982's user avatar
0 votes
0 answers
245 views

RS-485 Modbus keeps sending set timeouts. Is it normal?

I try to monitor RS-485 communication between Toyo motor drivers and an IPC control program. I monitor with a third-party software Device monitoring studio. The program is written by us. However, I ...
Superuser's user avatar
  • 169
0 votes
0 answers
299 views

How to record RS-485 Modbus communication at PC?

I am working on a system with an IPC, RS-485 Modbus communication, and 15 Toyo step motors and drivers. A motor frequently moves without IPC intentionally sending moving instruction and causes a ...
Superuser's user avatar
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0 votes
1 answer
74 views

RS485 UART Rx Receive Event Handler not fired for all Tx Commands sent [closed]

I am using (1)Azure Sphere MT3620 Starter Kit and (2)RS485 CLICK 5V and (3)Geovan Board Here is the setup (I don't have latest picture, so #2 is swapped to first slot in the MT3620) My MT3620 is ...
HaBo's user avatar
  • 101
1 vote
3 answers
6k views

Cable selection and wiring for RS485 communication

I'm designing a sensor system where each sensor communicates via RS485 MODBUS in a high-density environment. Each line consists of 18 sensors which then goes to a gateway (Elfin EE11) that converts ...
Max's user avatar
  • 557
0 votes
1 answer
231 views

Modbus acquisition timings

Part 1 What is the standard timing method for bits acquisition for a receiver using Modbus RTU? For example, for UART: "Communicating UARTs have no shared timing system apart from the ...
NinjaGreg's user avatar
0 votes
2 answers
2k views

MODBUS RTU reading on Jetson Nano over RS485

I'm trying to implement Modbus reading on Jetson Nano (Linux - Ubuntu operation system).System include 3 part: -MODBUS device which I would like to achieve input registers. --> Krohne Signal ...
Fırtına Hüseyin GÖKTAŞ's user avatar
0 votes
1 answer
71 views

Wired sensor bus technology

I am working on a project which requires a dozen VL53l0X I2C-TOF sensors to be polled by one master MCU over a few meters of cable. Thus, I decided to accompany each TOF by an Atmega8 acting as a ...
Daniel D.'s user avatar
0 votes
1 answer
137 views

Bus communication scheme for large number of devices (255+ nodes)?

I'm trying to figure out the feasibility of setting up some type of differential bus communication for up to 400 devices outdoors. The main constraints are mainly power consumption, complexity, wire ...
Jackson Seal's user avatar
0 votes
0 answers
173 views

Turn Node MCU into a PLC which is integrated Lora module for IoT application

I've built a PLC that supports Lorawan and Modbus protocol using Node MCU. I managed to make it possible with Modbus by using OpenPLC. Everything worked well apart from its limitation in the distance ...
Thanh Nhon's user avatar
1 vote
1 answer
197 views

RS485 communication issue

I have used PIC18F45k40 device for RS485 communication. I have 2 ckts one is isolated and another non isolated RS485 design. I have schematic & placement for reference. I have connected multiple ...
Ajit N's user avatar
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