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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.

Modbus is a serial communication 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.

See Wikipedia's article on Modbus for more information.

Note that Modbus has replaced its "master/slave" terminology with "client/server", respectively:

Modbus communications [are] characterized by communication between client device(s), which initiate communication and make requests of server device(s), which process requests and return an appropriate response (or error message).

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Handling register updates in Modbus systems

I am currently developing a Modbus RTU enabled system that consists of DSP and a microprocessor that handles the Modbus communications. The DSP is sending data to the microprocessor and the microprocessor provides Modbus interface to the DSP…
udushu
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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. This is a whole other story. We have all the…
James Mason
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Arduino as Modbus client with MAX485 doesn't get any response

I'm having some troubles trying to query a Modbus server with an Arduino through RS485. I've already succeeded in querying a software Modbus server running on my PC through the USB/COM port using the ModbusMaster libray, hence it shouldn't be a…
etuardu
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What is a conventional way to set a Modbus device address and baudrate?

What's a conventional way to set an address and baud-rate/parity on a Modbus device? Is this supposed to be done using hardware switches or can be done through a software? If done through a software, can this software be connected on the Modbus…
udushu
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RS485 without flow control

Is it possible to send/recieve on RS485 without flow control. I am working on stm32f4 platform with a MAX3160 multiprotocol transceiver(supports RS232 and RS485). The UART lines form STM32F4 are connected to the MAX3160. When the MAX3160 is…
Sumanth V
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Is the information in MODBUS function code 16 redundant?

MODBUS function code 16 is "Write Holding Registers". The function command structure is: Address (1 byte) Function code (1 byte) First register address (2 bytes) Number of registers to write (2 bytes) Number of bytes to follow (1 byte) Data (N…
jfowkes
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RS485 not working in pic24fj128ga202

I would like to send and receive data between two PIC24F microcontrollers via RS485. Here i'm using SP3485 IC. I've set one microcontroller as transmitter and another one has receiver. My microcontroller has 4 uart. One of the uart(here i use UART4)…
arun
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RxTx communication with multiple slaves using a RaspberryPi

I am a programmer trying to build a circuit with limited EE knowledge. With so many options(at least being new to this), just want to make sure I am going down the right path. What I am trying to build is a master device with a RaspberryPi and many…
VirtualLife
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RS-485 Modbus device to MCU

I have a device (an energy meter) that sends data via RS-485 (Modbus protocol). And I want to collect it with MCU. The important thing is that I'm trying to design a board and I want it to be scalable. That means I might have 1 device connected, or…
Andrejs Gasilovs
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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" through MODBUS protocol and then will gives these values to…
Niks
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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 that maybe(?) has benefit of cleaner code and…
JeromeBu1982
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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 (top is A, and the bottom is B). However when sending…
Lars Stenberg
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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: | Starting Address | Info | |------------------|-------------| | 0x0 …
Jastria Rahmat
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Besides address is there other limit on max nodes via RS485 Modbus-RTU

Since there is 1byte for nodes' address in Modbus frame, the limit should be around 256.But some say there is some limit on this scenario (RS485, Modbus-RTU) base on chips and wire. Chips support 32…
Shihe Zhang
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Best way to poll for Modbus RTU servers through a Modbus TCP gateway

I'm using a number of Modbus RTU devices connected to my PC through a Modbus TCP gateway. I'd like to poll all the available server addresses to check which ones are available through my program. What would be the best way to do this ?? I guess I…
Saad Farooq
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