What is the difference between CAN and 2-Can?

[Wendy Holladay]

We have been using CAN with the RS232 port successfully all summer and fall. I have been reading about 2-CAN but other than wiring can't see the difference. Is there one? Is one of them better than the other?

If we went to 2-CAN with the 4 port cRIO, would we plug the 2-CAN into one of the radio ports? The 1 Enet port on the cRIO is used by the radio.

[jwakeman]

The difference is bandwidth. With the serial configuation you are limited by the speed of the RS232. 2CAN lets you use ethernet with CAN bus and gets you something like 5 or 10 times the bandwidth. So if you can send send a command to the jaguar 10 times a second with the RS232 version, then you would be able to do it 100 times a second with 2CAN. Or if there were 10 messages that you like to send to the jaguar every second, 2CAN would let you send those messages 10 times a second.

[Mike Copioli]

Originally Posted by Wendy Holladay

We have been using CAN with the RS232 port successfully all summer and fall. I have been reading about 2-CAN but other than wiring can't see the difference. Is there one? Is one of them better than the other?

CAN is the communication protocol used to communicate with the Jaguars. The 2CAN is a gateway device used to bridge Ethernet to CAN. The Jaguars may also be used as a gateway between serial (rs232) and CAN. Below is a list of benefits to using the 2CAN gateway instead of the serial gateway.

- Bandwidth
- Integrated Web dash
- Diagnostics
- Simpler wiring
- Not driving a motor (Gateway is a much lower risk of failure when not driving a motor)
- Ability to view motor status via wireless while driving the robot.

Originally Posted by Wendy Holladay

If we went to 2-CAN with the 4 port cRIO, would we plug the 2-CAN into one of the radio ports? The 1 Enet port on the cRIO is used by the radio.

2CAN is two port Ethernet switch, (effectively a passthrough) This prevents a port on the cRIO from being tied up. However R53 requires:

[R53]
Connections to the cRIO Ethernet ports must be compliant with the following parameters:

A.The DAP-1522 wireless bridge is connected to the cRIO Ethernet port 1 (either directly or via a CAT5 Ethernet pigtail).
B.Ethernet-connected COTS devices or custom circuits may connect to any remaining Ethernet ports; however, these devices may not transmit or receive UDP packets using ports 1100-1200 except for ports 1130 and 1140.
So to comply with the rules the 2CAN would need to be connected to the wireless bridge. Either port on the 2CAN will work fine.

[jwakeman]

Originally Posted by Mike Copioli

- Not driving a motor (Gateway is a much lower risk of failure when not driving a motor)

What does this mean?

[Joe Ross]

If the black jaguar that you are using as a serial bridge browns out due to a spike in current in the motor it's driving, you lose the entire bus. The 2CAN has a separate power supply, so it isn't susceptible to that problem.

[Mike Copioli]

Originally Posted by Joe Ross

If the black jaguar that you are using as a serial bridge browns out due to a spike in current in the motor it's driving, you lose the entire bus. The 2CAN has a separate power supply, so it isn't susceptible to that problem.

Bingo.

[Bryscus]

Originally Posted by Joe Ross

If the black jaguar that you are using as a serial bridge browns out due to a spike in current in the motor it's driving, you lose the entire bus. The 2CAN has a separate power supply, so it isn't susceptible to that problem.

I somewhat disagree. The serial to CAN conversion seems to be a separate circuit. We have blown a few black Jags that don't respond at all but they still act as converters.

- Bryce

[Mike Copioli]

Originally Posted by Bryscus

I somewhat disagree. The serial to CAN conversion seems to be a separate circuit. We have blown a few black Jags that don't respond at all but they still act as converters.

- Bryce

If you damage the black Jag being used as the gateway to the point of affecting its 3.3v power supply you will absolutely lose the entire CAN bus.

[Bryscus]

Originally Posted by Mike Copioli

If you damage the black Jag being used as the gateway to the point of affecting its 3.3v power supply you will absolutely lose the entire CAN bus.

Mike,

I'm not saying it can't happen, only that my experience leads me to believe that you've got to screw something up pretty badly to make them stop working as a gateway. Often when the black Jags go, you can see the part that turned black. It isn't on of the regulators. At least not in our case.

- Bryce