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 communications many extensions exist to allow communication over other networks such as TCP/IP.

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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 ...
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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 ...
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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 ...
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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 ...
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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/...
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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 ...
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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 ...
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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 ...
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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 ...
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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. ...
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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,...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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RS485 Communication Issue Adm2483

I have Setup like this for my application. I have Transformer which gives out 12V 1A & 5V 500mA output.I have used isolated ADM2483 design where power galvanized isolated. Primary side 5v &gnd ...
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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 ...
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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 ...
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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 ...
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RS485 USB converter driver polarity

I have an RS485 USB converter connected with a temperature controller in the controller's datasheet it says that the 12 is (+) and 11 is (-) and in my USB converter there is A and B Am not sure the D+...
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Isolating an existing RS485 tranceiver

I have a heat pump with an RS485 interface. Via a simple RS485 chip. No isolated interface, no isolated power supply to it. I want to add a power meter at 400+ meter to it and want to properly isolate ...
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modbus register address vs. register number; absolute address vs. offset

I'm developing a Modbus Slave device, and I'm having a little trouble understanding how to name/address my registers. Let's say I have 2 Discrete Inputs and 2 Input registers. From Modicon standard, ...
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Is there any limit of how many commands it can be sent to modbus controller relay?

I have modbus controlled relay hooked to raspberry pi (using node-red) which depending on the condition sends "on" or "off" command every 5 seconds (24h/365d). I know that relays in general have its ...
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Exactly what is an RTU (Remote Terminal Unit)?

I find the Wikipedia article and other sources ambiguous and I find that the definitions are so broad that I don't know how and when to use the term "RTU". I would like to figure this out because I ...
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How to increase data through put of RS485 RTU?

I am using 20 sensor nodes, each has mpu9250 i2c, Arduino atmega328 MCU 8MHz and max485 chip in it, each slave has a unique id program. I have Arduino due as Modbus master with max485 chip, I hope ...
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Wrong output using SN75HVD10 (RS485)

Designing a modbus master using a STM32F030CCT6 and a SN75HVD10 (3.3V). This is the schematic When i send the following message from the UART: 01 03 00 00 00 06 c5 c8 I see the following scopes (...
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2 votes
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Using CANbus cable for RS-485

I have a question regarding an application with a Modbus RTU network. I would like to know if it's possible to use a CANbus cable instead of an RS-485 cable? Here is a picture of the cable:
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3 votes
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Is there some kind of standard of modbus input register?

As the title said, based on your experience, is there a such thing? If no, which are the most commonly used? for example in a sensor, the input registers as follows: ...
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RS485 Pull-up, Pull-down and single termination resistor

Currently I use for Modbus RTU via RS485 with a shielded cable length of about 5 meters and a bitrate of 19.200 bit/s. Wired are 680 Ohm pull-up (A->+5V) and pull-down (B->GND) resistors near to the ...
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Why lines A and B are HIGH when idle (rs485)

I'm using modbus RTU over RS485 for a project. I use a RaspberryPI as master and Arduino Pro Mini as slaves. My problem is the following : I plug a sensors on the bus and it returs its value. I plug ...
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Please help me understand modbus communications

I'm just starting out with understanding how modbus works over a rs485 protocol. I've received a communication protocol document from a company that makes solar inverters. I want to send a command ...
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Isolated Modbus (RS485) ground and UART noise

I build an isolated RS485 (Modbus) interface board for a sensor. I use ADM2682 as transceiver and VAQE6W-Q24-S12-D as isolated DC-DC converter. All is managed my a STM32L412. There is 2 interesting ...
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Can I use solid state output and relay output with the same components?

So I have a OTB1E0DM9LP Schinder Electric I/O distributed module and I want use it'output to control some 24v electro-valve's and some 24V contactors. The module have 2 Solid-state outputs of 24V 0....
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2 votes
1 answer
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Modbus: Sensors timed out when plugging another sensor

I have created an hydroponic system using modbus to communicate between a RaspberryPI server and plug&play arduino sensors. It works but as soon as I plug a sensor on the bus (physically), all the ...
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RS232 Modbus to USB wiring

I have a RS232 device that sends data following the modbus protocol. I have problems communicating with it and I think my wiring is wrong. Since most modbus devices work over RS485 it is hard to find ...
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Modbus RTU over RS232 link

I am designing a convertor board that will interface three device with Modbus RTU RS232 port to a Modbus RTU RS485 network. Slaves supports Modbus RTU, but their ports is different from master port. ...
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Trouble connecting to temperature controller using MODBUS,RS485 and MATLAB

I am trying to communicate with a temperaturature controller ATR-401 using MATLAB but i am having trouble just connecting to it and reading temperature data.I have set baud rate, data bits, parity and ...
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Detecting Communication Frames

I am sending data between a master and several slaves with RS485 with bytes (8 bit) messages with a very simple frame inspired on Modbus ASCII: ...
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Modbus slave firmware development

I'm developing a simple RS485 based MODBUS slave application on a Microchip PIC micro-controller and need to know best practices to follow on its application side. I can guide myself to get the ...
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1 answer
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Implementing Modbus RTU on a UART device

I have a particle counter HPMA115S0 which has a UART communication interface. I bought a TTL UART to RS485 Converter Module to make it work with a PLC over Modbus RTU protocol. I usually work with ...
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Why is there no reponse from ModbusRTU slave using converter?

There are two devices: Eaton EM20/M (~like Northern Design Cube 400) Volison ADM-5850G Connected them like: Trying to get data from EM20/M which supports ...
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2 votes
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RS485 registers for calculating total power consumption (kwh)

I have an energy meter (OHIO A2000) which has been now discontinued by the manufacturer. Anyway, I'm following the manual for extracting energy parameters through Modbus RS485 communication. I'm ...
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ModBus Timeout Error

Anyone very experienced with Modbus & RS-485??? My task is to control a DC motor using micro PIC24. The motor setting like the angle, delay, start/stop, duty cycle, etc will be sent from PC using ...
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