Nowadays many cars use ( Controller Area Network ) bus to connect them, but modern automobile computer control unit, the control unit to the system response time requirements are not the same. Some systems for the demand of real-time high command issued later, if not to the actuator response in time, it may cause serious and even fatal consequences, such as anti-skid brake control unit, an airbag, some systems such as lighting control, control of air conditioning on the system response time requirements are relatively low.
Due to more and more computer control unit, using a single network bus load is heavy, the author through structural high, low speed , on real-time computer control unit adopts high-speed network transmission; the other using low-speed network transmission, and by using the micro controller as a gateway. Make transmission line is greatly simplified, the reliability is greatly enhanced.
In two, the technical characteristics of bus
( Controller Area Network ) bus is a serial multi master controller area network bus. It has high security, reliability and real-time performance, simple and practical, low cost of network. Particularly suitable for the automobile computer control system and environment temperature, strong bad electromagnetic radiation and vibration large industrial environment. Communication media be twisted pair, coaxial cable or optical fiber, data transfer rate up to1 Mbits / S ( here the longest communication distance is 40m ). bus is widely used in automobile, shipbuilding, robot, building automation and other occasions.
Since since the advent of bus, bus protocol to meet various application needs, have appeared in several high level protocol. At present, most of the network based on bus based on bus protocol. open, DeviceNet and SDS are usually used in the protocol, suitable for any type of industrial control local area network applications, and CAL application based on standard application layer communication protocol optimization control of occasions, SAEJ1939 is used in trucks and heavy automobile computer control system.
Three, automobile computer control based on P87C591
P8xC591is a monolithic high performance 8 bit microcontroller, on-chip controller, from the 80C51microcontroller family derived from. It uses a powerful 80C51instruction set and the success of the included Philips semiconductor SJA1000 controller Peli function. All static kernel provides extended power-saving mode. The oscillator stop and recovery without loss of data. Improved1:1 internal clock prescaler in 12MHz external clock rate is achieved when the500ns instruction cycle. Micro controller to the CMOS advanced manufacturing technology, and design for automotive and general industrial applications. In addition to the standard 80C51characteristics, device for these applications to provide many special hardware functional. P8xC591 combination P87C554( controller ) and SJA 1000( independent of the controller ) function, and has the following characteristics: the enhancement of enhanced receive interrupt; extended acceptance filter; acceptance of” change on the fly filter”.
At present, the automobile computer control has been related to the power and economy performance, safety, reliability, purification and comfort and other aspects, including engine control, transmission control, cruise control, brake control, lighting control, air control, wiper control, instrument management system, and various control system electronic control unit ( ECU ) tightly interconnected, need for real-time data communication, the bus as a potential application of controller area network bus, in recent years in the automobile computer control system has been more and more widely used, and has become the main European automobile manufacturing industry standards, representative of automobile electronic control network of mainstream development trend.
Car pc manage program within many of these manage program with the MAY, 0line is really a real-time manage program system, the actual manage device instructions sent, need to ensure which inside a particular time period to obtain a reaction, or even there might be a dreadful incident, that demands the vehicle MAY conversation system getting greater baud price environment as well as dependability. Furthermore, the vehicle within the real procedure from the procedure, numerous nodes between your requirement for a lot of real-time information trade. When the entire automobiles of nodes tend to be connected inside a MAY system, a lot of nodes via a MAY coach with regard to conversation, info administration settings somewhat incorrect, is extremely simple to achieve the coach fill is actually too big, may cause the machine real-time reaction pace in order to decrease, that instantly program isn’t permitted. Consequently, all of us within the vehicle of every node within real-time tend to be examined, based on the ask for from the real-time needs, style associated with higher pace 2, an interest rate associated with various MAY conversation system. The actual real-time needs, higher dependability needs associated with high-speed MAY conversation system comprising nodes, another real-time needs tend to be fairly reduced nodes associated with reduced pace MAY conversation system, as well as setup the actual entrance would be the 2 price various MAY conversation system in order to hyperlink upward, recognize information discussing in between all of the nodes. The entire automobile conversation system topology framework because proven within determine 1.
Figure 1engine control, transmission control, safety control, anti-lock brake control ( ABS ), the control unit node is the modern automobile action of core components, the response time is strict, so in the design of the transmission rate of 500Kbps high-speed communication network. Air conditioning control, wiper control, lighting control and instrumentation control and real-time requirement of relatively low, the transmission rate is less than 125 Kbps of communication network, the main controller connected across the high, low speed two bus, and the nodes for data exchange, and the role of gateway, to realize network interconnection.
Electronic control unit of the micro controller ( P8xC591) via the data bus through a photoelectric isolator (6N137) and bus controller ( SJA 1000) directly connected, as the bus controller with a receiving buffer and a sending buffer, therefore, bus controller send port Tx0, Rx0, Rx1receiving port is respectively connected with the , bus send the receiver TxD and RxD, Vref port directly connected, _L and – H is bus two differential receiving and transmitting line. They are between the terminals respectively connected with a120 ohm bus matching resistor, when a node when the node occupancy of bus, the sending end ( level3.5 V ) after _H, the receiving end ( level1.5V ) by _L; when no node occupancy of bus, _L and _H on the level of both 2.5V.