1996-11-1 , E/IC-475/610
Technology News From Philips Semiconductors

Launch at Electronica 1996 on stand B4 in hall 24

Eindhoven, The Netherlands - 8 November 1996 - The increasing use of electronics in motor vehicles inevitably leads to a greater use of copper wire. More copper wire means more expense, greater weight, more fuel wasted, and more difficulty in tracking down faults. But a new technology, called CAN (Controller Area Network), is revolutionising car design by doing away with the myriad of copper wires within a car and replacing them with a simple twisted pair cable that encircles the inside of the car, in a similar fashion to a ring main in a house, to carry all the instructions. Small transceivers connect to the CAN and control the electrical control operations of the car, such as power train management, seat adjustment, mirror adjustment, door locking, and ABS braking. The CAN approach not only simplifies the wiring to make fault tracing much easier, but it also enables greater levels of comfort to be provided within the car as the centralised control means that all the seat and mirror settings can be pre-programmed for various drivers - it can even automatically change the radio to the preferred station.

CAN has already been designed into production cars. However, dependence on two wires does raise a safety issue in that problems might occur with the wires themselves being damaged. Philips Semiconductors is a leader in CAN technology and has invented a solution in the form of a unique fault-tolerant technology that is used its new  PCA82C252 CAN transceiver. This enables the CAN to keep operating even if one of the wires is cut or shorting because this system operates on relative changes in voltage, and thus provides a much higher level of safety. The PCA82C252 provides drive capability for up to 32 nodes over 40 metres of unshielded, two-wire cable at 125 kbps. Special emphasis has been placed on EMC performance, both reducing emission and increasing the immunity level.

The fault tolerance feature means that communications capability is maintained even if any of the ISO11898/ISO11519 wiring failures occur. The transceiver solves many common and frequent wiring problems such as poor connectors, but also overcomes short circuits of either transmission wire to ground or battery voltage, or between transmission wires. The transceiver resolves the fault situation without involvement of external hardware or software and its fault analysis results can be monitored via a status pin. In general, the fault detection circuit tolerates normal automotive system conditions, such as ground offset, EMC or leakage currents, and only reacts to physical damage along the transmission wires. The external bus termination network is distributed and redundant, and also allows for occasional disconnects.

The transceiver also addresses the requirement of system power reduction. The low-power mode reduces consumption to below 100µA.. In addition, a power output can even be used to disable the supply to the microcontroller and peripherals. In low power mode, the device is ready to receive remote wake-up requests via the bus or local requests via an input pin. Such requests initiate an interrupt to the microcontroller and/or an automatic activation of the power enable output, effectively provoking a system cold-start. Apart from the receiver circuit, a failure detection circuit also remains active in low power mode to prevent excessive battery discharge in case of short circuits.

Fail-safe circuit design prevents distortion of communication in a CAN system if a transceiver suffers from an on-board connection problem such as undefined input, poor Vcc supply, or ground or battery disconnection. The bus line drivers are short circuit proof to ground and battery, and implement a current limitation. The device tolerates jump start situations and transients up to + 40 V. Additional features are battery voltage monitoring and over temperature protection. The transceiver comes in an SO-14 package for the temperature range -40 to + 125³C. It is priced in the region of $1.50 in volume quantities.

Philips Semiconductors, a division of Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the eleventh largest semiconductor supplier in the world. Philips Semiconductors' innovations in digital audio, video, and mobile technology position the company as a leader in the consumer, multimedia and wireless communications markets. Sales offices are located in all major markets around the world and are supported by systems labs.