I have been running a spartan3 connected to my ms3x over CAN successfully for a while now. I am trying to add a CANgauge in between the two and it is not wanting to work. I went to measure the resistance between the CAN Hi and Lo wires at the node I added for the gauge and it is 120 ohm when it should be 60 ohm. This is telling me only one terminating resistor is active. I tested, power off, at the ms3x and got 120ohm. I realize the spartan3 resistor is an electronic resistor that needs to be measured power on. Either way when it’s powered on, no CANbus wires connected to the controller, it reads 120ohm for about 8 seconds then drops down to 0 ohms. Is this controller working correctly? Right now I don’t have a way to power the spartan and not my ecu, doing that should put both devices in a testable state for the terminating resistors. When I have both the ecu and spartan powered on and connected I am reading 160 ohm, although I’ve read this is a worthless measurement. The whole bus really needs to be tested in its “off” state (spartan3 powered so electronic resistor can activate, ms3x off as it’s a physical resistor). Any measurements done while the bus is powered and sending signals is no good.
Measuring the bus while powered is meaningless.
Without Spartan 3 connected, does the gauge work?