Controlled area networks
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0.* CAN is an information system that enables data to be transferred from one ECU to another. The central computer or vehicle information centre (VIC) sends messages around the network like e-mails: ECUs act on these messages or simply acknowledges receipt.
Working to the ISO standard (ISO 11898) and SAE J1939/71 means that all protocols are recognisable. This is important, especially from the bodybuilder and PTO manufacturer's viewpoint.
Inside the ECU is a processor, a CAN controller and a transceiver. Whether the ECU is controlling the ABS, engine management or an automatic gearbox, it attaches to the network via the CAN High and Low.
A CAN network can have as many ECUs as are required, all connected to two wires—CAN High and CAN Low—with a termination resistance to close each end of the loop. These counter any reflections when transmitting signals.
Oaf's digital instrument panel has been around since the mid-1980% until recently it needed about 40 different coloured wires, a speedo cable and air pipes for the various functions. The CAN-bus system only needs one plug with an earth lead, a positive wire, a black wire for the Davie socket and two High/Low leads that come into and leave the panel en route for other system ECUs.
So every new panel function, including the speedometer. rev counter, fuel gauge. temperature gauge, air-pressure gauges and all warning lights, is driven by digital signals supplied by the processor via the CAN bus. Even the driver's digital display unit is fed from the CAN bus: it offers functions from alarm clock calls to fuel consumption and metric conversions.
On older vehicles locating and measuring input signals vehicles meant finding the right loom diagram, identifying the required wires in a bulging loom by tab or colour, then locating the right plug.
New Oafs have a three-in-one CAN-bus network: vehicle (VCAN), information (ICAN) and EBS ((CAN) need just six wires: all data is stored in the vehicle information centre (1/11C).
Conventional components such as lighting and the new Smart alternator use hard wiring with a standard earth system. But the CAN network uses differential voltage between high and low. Working in milliseconds, it switches to CAN High at 3.5V then to CAN Low at 1.5V, leaving a residual 2.0 volts in between. The system works by continually switching on and off across various time scales to create a digital value that translates into a numeric signal code.
To illustrate the speed with which this electronic highway works, when a driver blips the throttle the rev counter's response is virtually instantaneous. In fact the rev counter is driven by the central computer acting on information received from the engine management system.
Data fed along the CAN-bus system operates the rev counter or tachograph, speedo. temperature gauge, indicators and fuel gauge. Digital sensors on the air system help to determine the air pressure too.
The launch of Oaf's newest CF models with their CANbus electronics has coincided with the launch of the third-generation Davie X0 diagnostic tool.
On the truck panel is a manual control switch (MCS) which enables the driver to scroll through the various headings.
The system offers permanent two-way communication. Press the button and immediately there's a stream of data passing to-and-fro with VIC talking to DIB to the tacho, to other various systems.
One benefit is that the driver doesn't have to do his daily checks in driving rain—they're done from the cab, by scrolling through the display panel. Instead of a dip stick there's a sensor in the sump that knows exactly how much oil is there, even to the point of waiting for the circulating oil to settle down first.
The XD's basic station has an LCD colour touch screen and combines a measuring and diagnostic instrument with a computer.