Vida CEM swapping

andrewgabler · Post by **andrewgabler** » 26 Apr 2023, 16:41

That is consistent with what I am seeing on my power supply, but I cannot read any of the can messages when hooked in with my arduino

andrewgabler · Post by **andrewgabler** » 26 Apr 2023, 20:04

I found someone who said this in the replies about the 120 ohm termination. Is this true? Could it be why I am not receiving anything?

The four 120ῼ terminating resistors go across the end node pins on the CEM.
CAN HS end node 1: CEM Pins D:31 & D:46
CAN HS end node 2: CEM Pins D:32 & D:47

CAN LS end node 1: CEM Pins D:35 & D:50
CAN LS end node 2: CEM Pins D:37 & D:52

T5Luke · Post by **T5Luke** » 27 Apr 2023, 04:40

Here this is minimum connection to CEM on bench.

On D connector:
Green: HS CAN-L to pin 14 OBD
White: HS CAN-H to pin 6 OBD

Grey (pin 6 ): GND
Yellow (pin 8 ): +12V
Blue (pin 15 ): +12V

Also it needs +12V on the both big connectors (big green power socket)

I just have 1 x 100 Ohm between both can lines, on bench, that is enough for me...

Post by **vtl** » 27 Apr 2023, 08:22

We need sticky comments on MVS...

andrewgabler · Post by **andrewgabler** » 27 Apr 2023, 17:30

This is driving me crazy. There must be something wrong with my hardware setup. I am using an arduino MKR wifi 1010 with a canbus shield. I am also using a arduino uno with a canbus shield. Neither one work with the software I wrote to read the CEM on the bench. I have checked the resistance with a multimeter, when the Arduino is connected and power to the CEM is OFF it reads 120 ohms. when the arduino is connected to the CEM and power is ON it reads nothing or all over the place Is this my issue?

As for the software, it works perfectly fine when I read the canbus high or low network with my car through the obd2 port.

I am currently using the arduinos to debug this issue, i do have the teensy 4.0, but am waiting on the mail for some bosch transceivers

this is happening on all 4 of my cems, 2 cem L and 2 cem H

Post by **vtl** » 27 Apr 2023, 19:55

I think your CEM falls asleep. Once power is applied you have about 20 ms to send it into programming mode. In programming mode it only replies to CAN requests sent to it, otherwise it stays silent. A proper bench setup that does not sleep should have DIM, I think?

andrewgabler · Post by **andrewgabler** » 27 Apr 2023, 20:06

So I wouldn’t even get a single message sent to me via canbus before it falls asleep? I have 3 dim’s and connectors sitting around to play with, I just hook them up to the can network and share the 12v source?

Post by **vtl** » 27 Apr 2023, 20:09

andrewgabler wrote: 27 Apr 2023, 20:06 So I wouldn’t even get a single message sent to me via canbus before it falls asleep? I have 3 dim’s and connectors sitting around to play with, I just hook them up to the can network and share the 12v source?

It sends a burst of like 6 messages or so. If you don't get that - something else is wrong. But your setup should be all set and listening when CEM comes up.

andrewgabler · Post by **andrewgabler** » 27 Apr 2023, 20:10

I am not receiving those messages

Post by **vtl** » 27 Apr 2023, 20:12

Share your code?