What does USB3 mean for the contol industry?

[Peter Nachtwey]

You aren't getting it.

OK, I get the point - the basics, anyway. But I don't get any feel for how significant the effect is. It sounds like a millisecond/sub-millisecond wait, which could be significant for high speed/realtime devices like motion controllers and PLCs.

These wait states happen for every access of the USB interface. Every byte that is read or written will incur wait states. That means every byte transfered wastes a whole lot of time and the CPU does nothing else while waiting. I will try to find out tomorrow how many wait states our Profibus DP chip has and how many wait states the USB chips has.

Aren't you always going to have a similar delay, or can you get closer to achieving a "straight to the wire" I/O connection with any modern high speed connections?

If one is willing to spend the money you can do what ever you want and get 32 bit access with zero wait states into a image table in dual port ram or dual port FPGA.

 

[JesperMP]

Why would you want your Ethernet cable to only have 4 wires?

At 100 Mbps, only the 4 wires are used. In Profinet cables you will only find 4 wires. And there are very few PLCs (I dont know any) that support Gigabit ethernet. Does Ethernet/IP support Gigabit ?

Some time in the future Gigabit will come even for PLCs, but I dont see the need right here and now. I prefer that the last of the arcaic serial busses be put to rest rather than going to Gigabit ethernet.

There are also similar connectors that use all 8 pins, but they are more cramped, and more expensive. So we stick with 4 wires for now.

 

[surferb]

As far as I know that's true (4 wires used) of GigE and probably 10 Gig. I thought the extra wires and twists were to mitigate crosstalk and attenuation. I don't see why Industrial cables wouldn't want this.

At 100 Mbps, only the 4 wires are used. In Profinet cables you will only find 4 wires. And there are very few PLCs (I dont know any) that support Gigabit ethernet. Does Ethernet/IP support Gigabit ?

Some time in the future Gigabit will come even for PLCs, but I dont see the need right here and now. I prefer that the last of the arcaic serial busses be put to rest rather than going to Gigabit ethernet.

There are also similar connectors that use all 8 pins, but they are more cramped, and more expensive. So we stick with 4 wires for now.

 

[JesperMP]

10 and 100 Mbps --> 4 wires
Gigabit --> 8 wires

wiki: "10BASE-T and 100BASE-TX only require two pairs to operate, located on pin 1 + 2, and pin 3 + 6"

wiki: "1000BASE-T uses all four pairs bi-directionally and the standard includes auto MDI-X"

 

[surferb]

OK, fair enough. Congrats on your 7k mark!

 

[JesperMP]

OK, fair enough. Congrats on your 7k mark!

I didnt even notice that myself !

Thanks !