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which one, Can-bus, MOD-bus, I2C, RS232, RS485

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rudie

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difference between can bus and modbus

Hello guys,

I don't know what to use as communication protocol. On the internet i could find come information about them but not enough. I know that the difference between RS232 an RS485 is mainly that with RS485 you can use a longer cable length. But if i then read somting about MODbus i see that MODbus also uses the RS232 or RS485 communication protocol. The communication with the RS232 and RS485 is always between to units, a receiver and a transmitter. The other ones (Canbus,MODbus and I2C) can let multiple units communicate(master and slave communication) with each other. But what are the main differences between those three? I know that MODbus is mostly used in PLC communication but why? and why not I2C or Canbus?

i hope that someone can explain this to me.

greets Rudie
 

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diff bet i2c and rs232 communication

If you don't know which protocol to use, you probably don't need any, cause your application doesn't require a protocol. I wouldn't reagard RS323 or 485 as a protocol, it's a physical a physical layer used in a protocol.

I2C is a different pysical layer together with a specific protcoll, but's it's completely inappropriate for communications outside a device respectively for distances above 1 m.

Also CAN uses a specific physical layer different from RS232 or RS485, for this reason it always requires a special controller hardware.

MODBUS in contrast is protocol, that can use any RS232 or RS485 hardware, either on a PC or in an embedded processor. It also is rather simple, that's why it's popular, I think. It's a defined open standard (originated from Schneider) to pass data (single bit digital and 16 bit "analog") between one master (or client) and many slave (or server)
stations. It's particular useful when you intend data transmission to or from devices from different vendors.

When you don't need to be compatible to any existing standard, you not necessarily need a complete protocol, just a definition, in which format you transmit data. You could e. g. print measurements in text format to a serial line, in a format that could be displayed on hyperterminal for a human reader or printed to line printer. But it may be read and interpreted by a computer as well. A lot of devices sending data on an interface work this way.
 

ckshivaram

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dont re-open very old threads... Check the date of the thread before you reply......

---------- Post added at 09:28 ---------- Previous post was at 09:27 ----------

your reply is no way related to the thread... Understand the requirement of the poster and then post your reply
 

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