pic: cRIO CAN Jag

[s1900ahon]

Originally Posted by biojae

i just noticed in the picture that there is a split cord at the base of the cRio, one side goes to the jags and the other goes to an enclosure, is that another termination resistor?

Yes, but that shouldn't be surprising. The CAN bus uses 2 termination resistors, ideally located at each end. Both termination resistors are 120 ohm. Neither the Jaguar nor NI-9853 (*) provide internal termination since they make no assumptions regarding the bus topology nor where they are placed.

(*) This module was used by NI on NItro.. but I would not make any assumptions about this. NItro is a technology demonstration vehicle.

[s1900ahon]

Originally Posted by biojae

It looks like it could be made easily, how much does NI sell it for? (We will probably get one in the kit though)

Also what module # is in the cRIO?
I know that the jags can do 1mb per second comms, and there is a 1mb module but there is the possibility of us having the slower comms, (Though i don't believe that we will ever need to have that much data throughput)

The cable pictured is not available from NI. It was a small custom build for NItro. It is a small piece of 9 conductor ribbon cable with 4 flat ribbon DB-9 connectors crimped on it. One DB-9 is used for connecting to the Jaguars, one for connecting a termination resistor, one to connect to the NI CAN module, and the final for connecting a CAN bus analyzer. The parts are cheap and no soldering required.

A comment on the bus bandwidth.. the number of packets per second you can get on CAN depends on a number of factors. If you consider a 29-bit message identifier (as used by Jaguar) and average bit stuffing, on a 1 Mb/s network, you can get >12,800 1-byte packets per second and >9,300 4-byte packets per second. I bet that some crazy team will be complaining in a year or so about the need for more CAN bandwidth . The nice thing about CAN is that there are no collisions, so you know when it is busy the data still gets through.

[biojae]

I just wish that first would tell us that we can use the CAN bus in 2010

[biojae]

Though at atlanta, the luminary micro and java people said that the Fpga image was gettting too large and they (WPI) would have to take some functionality out to get CAN in