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.

15 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
2
votes
0answers
136 views

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 ...
1
vote
2answers
44 views

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, ...
1
vote
0answers
64 views

Looking for data sheet of the following Modbus Sensors #updated

I'm a noob in this area, please ignore any stupidity and lack of info and any help is appreciated and I'm ready to provide all clarification on the post if by chance any info is missing. So i have ...
1
vote
0answers
685 views

watchdog timer on PLC

I've currently set my PLC as a modbus slave, and written some python code which connect to it and act as a modbus client. I am having some problems with the modbus server sometime terminating the ...
0
votes
0answers
26 views

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 ...
0
votes
0answers
165 views

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 ...
0
votes
1answer
129 views

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 ...
0
votes
0answers
46 views

Comunicating with Servo Driver using MODBUS

I am very new to MODBUS and am having trouble connecting to my Servo Motor Driver. I am using a Yun Duan A2 that I purchased from Aliexpress so I could learn about controlling Servo Motors using ...
0
votes
0answers
59 views

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 ...
0
votes
1answer
238 views

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 ...
0
votes
1answer
45 views

Interface PID temperature control module using Arduino

I need to interface a modular type temperature controller using Arduino. This is the datasheet of temperature controller The datasheet mentioned like this, My questions are, How can I interface( ...
0
votes
0answers
511 views

Modbus RTU for FPGA

I need to implement Modbus RTU in FPGA (Cyclone 3). Basically I see two ways to do that. The first one is to hardcode it in VHDL and it doesn't seem to be that hard at the begining. But I have looked ...
0
votes
0answers
314 views

libmodbus modbus_read_bits() returns illegal function

It is all okay when it comes to read registers with: modbus_read_registers(ctx,0,32,destination); It gives me values of 32 different registers. But when it comes ...
0
votes
2answers
446 views

Modbus communication between Arduino and Unitronics Jazz2 PLC

I am trying to connect Unitronics Jazz2 PLC (JZ20-R16) and an Arduino Uno using Modbus protocol, over RS232 interface. I've got all the required connectors for both Arduino (TTL-RS232 MAX3232 ...
0
votes
0answers
219 views

Modbus RS485 trouble

I'm trying to connect a power meter (http://www.ebay.co.uk/itm/272572704122) with Modbus over a RS485-USB converter (http://www.ebay.co.uk/itm/231570466384) The converter looks like a serial port (<...