I'm trying to connect the mBed to a device controlled by a Fujitsu MB90F549. This unit runs at 12v.

I've tried to use a mcp2551, but the mBed/mcp2551 combo delivers canH/canL signals based on the USB 5v and the Fujitsu unit uses 12v.

Does anyone have a possible solution for this problem ?

The CAN bus operates on differential voltage up to 4volt differential.  The CAN bus does not run at 12V.

The Fujitsu MB90F549 looks like a proprietary micro controller that has two CAN controllers.

From the Fujitsu MB90F549 data sheet:

The MB90540/545 series with FULL-CAN*1 and FLASH ROM is specially designed for automotive and industrial ap-

plications. Its main features are two on board CAN Interfaces (one for MB90V545 series), which conform to V2.0

Part A and Part B, supporting very flexible message buffer scheme and so offering more functions than a normal

full CAN approach.

You just need to connect a CAN transceiver like the MCP2551 to the Fujitsu MB90F549 and another one to the mBed.  Then connect CANH and CANL from each MCP2551 together through twisted pair wire.  If these are the only two nodes on your network you will need to put a 120 ohm terminator resistor between CANH and CANL at each MCP2551.

Thank you for the quick reply. The unit in question is an Audio 10 CD Player  taken  from my car (a Mercedes W639).

While the unit is mounted in the car and working properly I measure 0 and 12 vold at pins C1 (canH), C2(canL)

Background info:

---------------------------

The Becker unit (BE6019.. Cassette player instead of CD player):

User manual. Pinout at page 22: http://www.perfectmarketaudio.com/Audio_10%20Manual%20PDF.pdf

Schematics: http://codedradio.info/manuals/becker/BE6021-schematic.pdf

The BE6021 processing unit with CAN support:  http://eedatasheet.com/pdf/MB90F549,FUJITSU,123793.pdf

The canbus transceiver: http://www.ec66.com/market/sheet/TJA1053.pdf

Why can not the CAN bus run at 12 volt ? The mcp2551 works for DC between -42 volt and +42 volt....

Curious two how did it end?