Profibus / Modbus

Hi all just a quick one what is Profibus and Modbus , are they just types of remote I/O and if so what's the difference

Thanks Jezz

ModBus is open protocoll. Profibus is nice try of FieldBus, no multimaster, master-slave polling system, no COS cababilitys, no multicasting, no broadcasting, no etc..
FieldBus must be more than RIO-bus, purpose is remote intelligence to field-devices as VFDs, abs encoders, control-valves etc..

See the documentation

seppoalanen said:

ModBus is open protocoll. Profibus is nice try of FieldBus, no multimaster, master-slave polling system, no COS cababilitys, no multicasting, no broadcasting, no etc..

Click to expand...

Get the real info at:
Profibus Trade Origanization

Profibus DP has a multimaster capability. It has a means of passing a token from one master to the next so only one master controls the bus at a time.

Master-slave polling is basic. A SST profibus master can update 6000 I/O points a millisecond using polling. ( The data exchange state )

I agree with the no change of state capability, but Profibus DP doesn't need it as it is so fast.

Profibus does have the something like mulitcasting/broadcasting in DPV2. I haven't seen a master that implements it yet.

Profibus also has isochronous data transfers.

The problem is that few of the master implement more than the basic features. Even worse is that many don't implement the basics correctly and the Profibus Trade Organization does nothing about it.

We are building a new product now and are making a Profibus DP interfaces. The problem is that there are a lot of features Profibus DP supports but there is not point in implementing them if the masters don't support these features. This is why many think Profibus DP can't do this or that. The real answer is that most don't need the extra features and it costs money to implement them.

Modbus is not a field bus. It is a protocol. Some have combined Modbus with RS485 which works well.

Modbus Plus is a field bus that has most of the features Seppo mentioned above. It was way ahead of its time. Modbus plus is great for talking between intelligent devices. Until Ethernet/IP, Modbus Plus was one of my favorites.

See Modbus.org