PLc Basics , a newbies PLC understanding

[tguclu]

Hi again ,

I think this post can be useful for newbies like me and avoid "future newbies" asking the same questions to you.But in order do that we need proffesions like yours answers

I want to ask some questions about ModBus and just to show you they i'm not a lazy man who asks everytgin to others i want to prove some of my knowledge.

First of all ModBus is a technogly came up with Modicon.But Schneider bought Modicon.As I learnt it means "RS 232 / 485 networking between PLC's" and it's a standart(like EIa for RS-232).

Let's suppose a situation with 3 PLC's regardless of their producer.2 of them ,let's say 30 metres distance ,and the 3rd is 1km far.Can I use Modbus protocol(ModBus ASCII or ModBus RTU) between 1st and 2nd PLC's.And connect 3rd PLc to other by ModBus TCP/IP protocol.Or to pass from (232/485) protocol to TCP/IP isn't allowed?

Second question is ,what's Siemens solution for ModBus?Is Profibus exact of ModBus ?

Thanks ,I will keep asking..

 

[Tom Jenkins]

Modbus RTU on a serial network is a master/slave protocol. One PLC must initiate all communications, read the data from the source, and then send it to any other PLC that requires the information.

Modbus Plus is a peer to peer protocol. Any PLC can request information directly from any other PLC or device on the network.

Ethernet is also peer to peer.

Digi and other companies make "bridges" that allow conversion of serial (RS232/485) communications to ethernet, but you need drivers to support the ethernet side.

Profibus and Modbus are different protocols that are incompatible and cannot coexist on the same serial network.