Nick B said:I think a better comparison would be Profinet vs Modbus TCP/IP.
i believe you're right... anyways.. i'm gonna create a new thread for that coz i have several questions...
Nick B said:I think a better comparison would be Profinet vs Modbus TCP/IP.
Peter Nachtwey said:The collisions can be largely avoid by using expensive switchs. The more expensive switches are necessary with protocol like Ethernet/IP were the slave devices can produce data on their own.
Peter Nachtwey said:Way too slow for many applications. DeviceNet may not be too slow for the OP. For motion control I find DeviceNet too slow unless the motion controller or drives are very smart.
Peter Nachtwey said:It TCP has an error it will retry to send old data.
There should be a Modbus/UPD as part of the standard.
What the message size of Profibus?Peter Nachtwey said:Profibus retries with new data. Profibus DP's weakness is its lack of ability sending messages or large amounts of data.
Smarter? How?Peter Nachtwey said:DeviceNet is smarter but MUCH slower. Profibus DP wins by brute force ( higher bit rates 12 MB vs 500K ).
That can be one way. That is called store and forward. When a slave produces data on the network it goes to every other device unless you have a managed switch were the data can be configured to go to just the nodes that need the data.danieluy said:ohh...
Basically how does the more expensive switches avoid this? by internal BUFFERING?
If devicenet can be set up so the slave only generated data on a change of state then devicenet can be fast and challenge Profibus DP. Profibus DP is dumb because it sends all the data all the time but the Profibus network is so much faster. I/my customers have had good luck using Profibus to control over 100 axes of motion control. I had to start and stop all the axes at the same time. I couldn't afford delays so that one axis would more before the other. Profibus DP made it possible to move all the axes together."OP"?
yes, you are right the data gathering of DeviceNet is too slow... i'm only using it to change speeds and such... So is "ProfiBus/ProfiNet" better at this? faster response times?
I don't know about ProfiNet yet. It is on our development schedule.that's cool for Profibus. is this the same with ProfiNet?
Profibus DP claims to be able to send 244 bytes of IO. It can but the data will not be 'consistent'. That means the data may not update all at the same time. This mode is not useful for motion control where the command and the data must be sent at the same time. It would be a disaster to send a command with another command's data. Profibus DP can only send 64 words with data consistency. That is why we have 64 word limits on our older 16 bit controllers and 32 32 bit words limit on our 32 bit controllers.What the message size of Profibus?
Is it 500bytes for Modbus TCP/IP?
Device can be smarter by configuring the slaves to send data on a change of state ( COS ) instead of all the time. Profibus DP sends all the data all the time but the Profibus DP's bus speed is MUCH faster and its packet efficiency is much higher.Smarter? How?
I don't know now. I have the specifications and equipment necessary to implement all these protocols. I don't think you want to buy the specifications. They aren't light reading. The ProfiBus/Net guys can't write a clear specification.are there any good articles that discusses about these standards?
Is isochronous Ethernet required for general I/O as per the OP's needs? I don't think so.LadderLogic said:Does EtherCAT somehow fits into this discussion?
Peter Nachtwey said:When a slave produces data on the network it goes to every other device unless you have a managed switch were the data can be configured to go to just the nodes that need the data.
Peter Nachtwey said:I/my customers have had good luck using Profibus to control over 100 axes of motion control.
Peter Nachtwey said:This mode is not useful for motion control where the command and the data must be sent at the same time. It would be a disaster to send a command with another command's data.
Peter Nachtwey said:Profibus DP can only send 64Words...
Modbus and Modbus/TCP..... MSTR block limits the transfers to 100 or 120 words... A AB MSG block can send 32768 words in one command. However, that data is actually sent in smaller blocks.
Peter Nachtwey said:Device can be smarter by.... send data on a change of state ( COS ) instead of all the time. Profibus DP sends all the data
Peter Nachtwey said:I don't think you want to buy the specifications. They aren't light reading. The ProfiBus/Net guys can't write a clear specification.
If the data is 'consistent' then it all data will be sent and received at the same time. This can only happen with Profibus DP if the packets are 128 byte, 64 words or 32 dwords or less.danieluy said:Why is this so? isn't the Command and the Data within the same packet? so it should arrive within the same packet.
It was my belief that an unmanaged switch also achieves this.When a slave produces data on the network it goes to every other device unless you have a managed switch were the data can be configured to go to just the nodes that need the data
For Modbus/TCP it does. For the multicast of Ethernet/IP it doesn't.GeoffC said:It was my belief that an unmanaged switch also achieves this.
Profibus DP doesn't need to because it only supports level 2 which is equivalent to sending raw Ethernet packets like the Host Engineering Protocol that AD uses. However, that also is a limitation too. There is no messaging. Just packets. This is a limitation when my customers want to download 8K dwords of graphing data.Another point for any Ethernet based system are the additional services provided at the lower level of the protocol stack. Examples being 'plug and play' of devices, faulty device replacement, network statistics, ftp file transfer, device address resolution (ARP), device address assignment (DNS and DHCP), CIP also provides a significant number of extra services. These are all provided as services, no extra effort required.
Not all of the Ethernet systems support all of the above, but I am pretty sure profibus supports even less.