Vida CEM swapping

[MaxDenisov]

K-Line TX to TX3 (pin 14).

Also this chip is obsolete (out of production), you may want to replace it with mc33290d.

Replaced to 33290d:

[vtl]

We have learned over time that the schematic needs relatively a lot of power. A few folks were failing cracking the PIN until they provided a better power source and/or used thicker wires. I think you may want to do something about ground and power on your PCB. I use 24AWG (d=0.5 mm) copper wires from CAT5e cable.

Also T5Luke claims the buses are already terminated in other modules, so resistors are not required in OBD-II case. I can't attest to that, maybe leave them not soldered? Or have jumpers like on many Arduino CAN-bus shields.

[RickHaleParker]

We have learned over time that the schematic needs relatively a lot of power. A few folks were failing cracking the PIN until they provided a better power source and/or used thicker wires. I think you may want to do something about ground and power on your PCB. I use 24AWG (d=0.5 mm) copper wires from CAT5e cable.

Thinking of making some heavy Solderless breadboard U-shape jumpers out of plastic coated paper clips. Tedious work but works great when done. Did this decades ago. Wish I had kept track of them.

Also T5Luke claims the buses are already terminated in other modules, so resistors are not required in OBD-II case. I can't attest to that, maybe leave them not soldered? Or have jumpers like on many Arduino CAN-bus shields.

Look for a chip resistor marked 121. 12 X10^1 Ω = 120 Ω . Electrically, It will be across the CANH and CANL outputs.

[vtl]

Look for a chip resistor marked 121. 12 X10^1 Ω = 120 Ω . Electrically, It will be across the CANH and CANL outputs.

Yes, the point is it might be not needed for OBD case, since the buses are already terminated in other modules. Extra resistor only weakens the signal and makes fronts less sharp.

[RickHaleParker]

K-Line TX to TX3 (pin 14).

Why not go ahead and do K-line RX to RX3 ( Pin 15 ) for future projects.

[vtl]

Why not go ahead and do K-line RX to RX3 ( Pin 15 ) for future projects.

This will be our paid feature unlock

Yeah, makes sense.

[RickHaleParker]

Look for a chip resistor marked 121. 12 X10^1 Ω = 120 Ω . Electrically, It will be across the CANH and CANL outputs.

Yes, the point is it might be not needed for OBD case, since the buses are already terminated in other modules. Extra resistor only weakens the signal and makes fronts less sharp.

You talking modules, ready made circuits on a PCB, or chips with a internal termination resistor? You need 120 Ω at each end of the physical CAN bus. One end of the physical CAN BUS is the CAN transceiver,

[vtl]

You talking modules, ready made circuits on a PCB, or chips with a internal termination resistor?

CAN-bus has to be terminated on both ends: at CEM and the farthest module (the one having the longest wiring to CEM). Now:

1. If OBD plugs in into real CAN-bus - OBD device does not need termination.
2. If CEM has a dedicated CAN controller just for OBD - it needs termination.

I always thought 2 is the case (CEM has a controller just for OBD), but T5Luke thinks differently.

[RickHaleParker]

You talking modules, ready made circuits on a PCB, or chips with a internal termination resistor?

CAN-bus has to be terminated on both ends: at CEM and the farthest module (the one having the longest wiring to CEM). Now:

1. If OBD plugs in into real CAN-bus - OBD device does not need termination.
2. If CEM has a dedicated CAN controller just for OBD - it needs termination.

I always thought 2 is the case (CEM has a controller just for OBD), but T5Luke thinks differently.

The CEM has more then one CAN bus port.

The OBD2 diagnostic connector is a separate physical CAN bus. The only two things on this specific CAN bus is the OBD2 diagnostic connector and a CAN bus port on the CEM. I posted the schematic showing this on a previous page. It shows the same thing in VIDA when you look at the network configuration under diagnostics.

The OBD2 connector has no termination resistor because it is not at the of the CAN bus. The diagnostic interface is the end of the physical CAN bus.

The reason they are at the end of physical CAN bus is because they are there to absorb reflected signals.

[RickHaleParker]

CT = Communication Tool.