You are not registered yet. Please click here to register!

plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!

Go Back - Interactive Q & A > - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Thread Tools Display Modes
Old November 17th, 2017, 09:52 AM   #1

Kataeb is offline
Join Date: Jan 2007
Posts: 447
" RS485 serial " or " Modbus Rtu " protocol

Kindly, what is the difference between " RS485 serial " and " Modbus Rtu " communication protocols? Like the below two modules, they use which protocol?



"character may be manifested in the great moments, but it is made in the small ones"
  Reply With Quote
Old November 17th, 2017, 10:14 AM   #2
United States

damica1 is offline
Join Date: Aug 2015
Location: Illinois
Posts: 595
RS-485 is just the means of the electrical transmission (it is a balanced signal), Modbus is the protocol at which the DATA is transmitted across the line.

You can transmit/receive Modbus across various electrical schemes
David M. Camp

Marshall Electric /

Please Download from our download section "Monitor and Control" .pdf.
  Reply With Quote
Old November 17th, 2017, 04:41 PM   #3
United States

danw is offline
danw's Avatar
Join Date: Oct 2004
Location: midwest, USA
Posts: 2,833
Modbus RTU has specific timing requirements that define the size of a communications message 'packet' and calculates the CRC error checking value.

Converters like these generally have a specific Modbus model with firmware that handles Modbus packets. The firmware is specfically designed to keep a Modbus message packet intact, without splitting it up, it constructs a proper Modbus packet from other data with the correct header and byte count values, and it calculates the CRC error check value for the Modbus packet.

The generic RS-485 is just that, RS-485. It does not hold to Modbus packet size and timing requirements or calculate a CRC value. It just transmits and receives on 485.
  Reply With Quote
Jump to Live PLC Question and Answer Forum


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
How to Implement Modbus TCP Protocol Using VBA with Excel gclshortt LIVE PLC Questions And Answers 14 June 18th, 2017 10:16 AM
MODBUS RTU <--ethernet--> MODBUS RTU farhanm LIVE PLC Questions And Answers 1 January 27th, 2016 04:34 PM
Ethernet TCP/IP and Allen-Bradley CompactLogix (RSlogix 5000) CAAJ LIVE PLC Questions And Answers 14 December 18th, 2015 12:46 PM
Modbus rtu with rs485 abbas.a.fahes LIVE PLC Questions And Answers 5 March 24th, 2015 07:47 PM
PLC 5 and Modbus RTU Steve Cav LIVE PLC Questions And Answers 3 September 18th, 2012 03:21 PM

All times are GMT -5. The time now is 10:22 PM.