Multiplex

This image shows a high-speed CAN, (Controller Area Network), data bus signal. This type of CAN signal can run up to 1 mbit/s depending on the physical length of the circuit. I have included a ‘maths’ channel to show the differential voltage at 0 to 2 volts, which is normal. The ‘maths’ channel can be useful when testing CAN, because it cancels out any noise that may confuse real-time analysis. The twisting of the wires means that any interference that takes place on one wire, will take place on the other.

can-is
CAN high-speed (ISO 11898-2 / CAN-C) 500 kbit/s with differential channel

The next couple of images are of the ‘PSA’ (Peugeot / Citroen) proprietary ‘VAN’ (Vehicle Area Network), system.  They are taken from the ‘VAN Body 2’ network, which is responsible for the door modules etc.  You can see that when the network is dormant, it sits at just below battery voltage.  When a ‘wake up’ signal is sent to the system, the voltage level drops to 0 to 4 volt signal.  In fact it is closer to 1 to 4 volts.  Unlike the Bosch High speed CAN system, the VAN does not use a differential signal, but instead it uses 2 lines of mirror image data. It is fault tolerant and can run with only 1 line operating, although in a downgraded mode, similar to that of the Bosch Low speed CAN.  It also utilises the twisted pair interference suppression method of wiring.  It does not have ‘end line’ termination resistors.  This system dates back to the early 1980’s and is therefore a pretty slow system.  The network illustrated here is a 62,5 kbit/s network.  The faster VAN Comfort network, responsible for audio and navigation etc. runs at 125 kbit/s, but has exactly the same system operation.  It started being phased out around 2005 and replaced by the more commonly used Bosch Low and Intermediate speed CAN.

VAN network switch on
PSA VAN Body 2 62.5 kbit/s network
VAN network data packet
PSA VAN Body 2 62.5 kbit/s data packet

This image is of the BSD (Bit Serial Data), communication line for the pre-heat relay, alternator and intelligent battery sensor fitted to BMW vehicles.

It is a battery voltage signal that runs at approximately 1kHz.

BMW IBS
BMW BSD (Bit Serial Data)