EtherCat vs Modbus

Now that Modbus has been included in the Power PMAC what are the relative strengths of each option, excluding servos? Is either one easier to program? Ladder support?

I've not used the modbus option, but I have heard that it has some delays. Typical modbus devices I've used (on other systems) max out at 5ms between polling, but I think this is totally dependent on the master implementation. I suspect the modbus implementation is a non realtime driver (aka standard linux ethernet) because I don't think Delta Tau is using a xenomai ethernet driver as of yet (I could be wrong). If this is correct I wouldn't rely on it for any kind of realtime performance.

 

EtherCAT on the other hand can be done at the microsecond level. Beckhoff boasts a 30us update cycle, but practically speaking I'd expect somewhere between 125us and 500us based on what I've heard from the guys at Delta Tau. Beckhoff does have EtherCAT IO that will respond this fast too, they sell their inputs with either a 30us or a 3ms filter I believe (check their website). EtherCAT will be deterministic whereas modbus is based on TCP and is not.

 

Any hard facts about the modbus implementation would be nice to see. :o) I could see it useful for comunicating to VFDs or other things where it is more of a setup change rather than a critical high speed operation. It all depends on what you need, of course.

 

KEJR

EtherCAT is a dedicated realtime network with its own network card that Delta Tau provides when the EtherCAT option is purchased. Transfers are performed during the servo cycle and it is highly deterministic.

 

Modbus TCP is a software protocol on top of generic TCP sockets. It is non deterministic but can use one of the CPU's ethernet adapters.

 

The system setup provided in the IDE already does EtherCAT generic I/O.