Vida CEM swapping

Post by **vtl** » 26 Apr 2021, 08:36

RickHaleParker wrote: 26 Apr 2021, 08:24The 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.

The schematics only shows pinout of the CEM. It says nothing about real CAN topology within Renesas.

One thing that speaks against that dedicated CAN theory is that if OBD device mismanages CAN settings - the whole car goes mad: clicking relays, tons of communication errors in many modules. Would that be on a separate CAN bus - that can't happen.

Post by **RickHaleParker** » 26 Apr 2021, 08:40

Perhaps we need to stop talking the CAN bus, which implies there is only one and start talking a Can bus which implies there is more then one CAN bus.

Post by **RickHaleParker** » 26 Apr 2021, 08:53

vtl wrote: 26 Apr 2021, 08:36 The schematics only shows pinout of the CEM. It says nothing about real CAN topology within Renesas.

One thing that speaks against that dedicated CAN theory is that if OBD device mismanages CAN settings - the whole car goes mad: clicking relays, tons of communication errors in many modules. Would that be on a separate CAN bus - that can't happen.

Count the CAN ports and see what is on the ones on the right side of the CEM.

Post by **vtl** » 26 Apr 2021, 08:58

Question closed.

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Post by **RickHaleParker** » 26 Apr 2021, 09:09

A physical CAN bus is a length of twisted pair and nothing more. 120Ω at the end of each twisted pair.

Post by **RickHaleParker** » 26 Apr 2021, 09:24

vtl wrote: 26 Apr 2021, 08:58 Question closed.

That is protocol layer not physical layer. There is a difference.

MaxDenisov · Post by **MaxDenisov** » 26 Apr 2021, 09:24

Added jumper pads and RX to 15 pin:
Gerber attached.
@vtl I can assemble and send spare pcb to if needed

: VCC11_1.png (35.91 KiB) Viewed 1261 times

: VCC22_2.png (101.26 KiB) Viewed 1261 times

OBDII used from ali: Type 1:

: OBDii.png (114.49 KiB) Viewed 1254 times

Post by **RickHaleParker** » 26 Apr 2021, 09:51

MaxDenisov wrote: 26 Apr 2021, 09:24 Added jumper pads and RX to 15 pin:

You might want to consider Transient Voltage Suppression ( TVS ). One spike over 45V on the 12V line would fry the MC33290. That Zener diode connected to +Vbat on the first page of the MC33290 Datasheet is TVS.

Post by **vtl** » 26 Apr 2021, 10:37

RickHaleParker wrote: 26 Apr 2021, 09:51
MaxDenisov wrote: 26 Apr 2021, 09:24 One spike over 45V on the 12V line would fry the MC33290.
One spike over 45V will fry half of the car. I looked at overvoltage protection in a few modules back in years, they were rated for up to like 30V.

Post by **RickHaleParker** » 26 Apr 2021, 13:09

vtl wrote: 26 Apr 2021, 10:37 One spike over 45V will fry half of the car.

It depends on the duration of the spike. It is energy not voltage that cooks.

..... Oh you mean half the electronics not 1/2 the car.

I looked at overvoltage protection in a few modules back in years, they were rated for up to like 30V.

From the datasheet: VBB(LD) 45 V.

What the heck ... The Internal Block Diagram shows internal TVS, 50V on the VBB, 10V on TX and RX. Why they put a TVS on the front page Application Diagram? Shall we assume the Internal Block Diagram is correct?