【正文】 } } } } 34 英文翻譯與中文資料 Foundation Of MCU The Central Processing Unit Although referred to as the brain of the system, the Central Processing Unit in a normal installation is the unsung hero, buried in a control cabi, all but fotten. Basic Functionality In a programmable controller system, the central processing unit timely control execution. It rapidly and efficiently scans all of the system inputs, examines and solves the application logic, and updates all of the system outputs. In addition, it also gives itself a checkup each scan to ensure that its structure is still intact. In this chapter we will examine the central processing unit as it relates to the entire system. Included will be the various functional blocks in the CPU, typical scan techniques, I/O interface and memory uses, power supplies, and system diagnostics. Typical Function Block Interactions IN practice, the central processing unit can vary in its architecture, but consists of the basic building block structure illustrated in M e m o r yO u t p u t sI n p u t s P o w e r s u p p l yP r o c e s s o r CPU block diagram The processor section consists of one or more microprocessors and their associated circuitry. While it is true that some of the older generation programmable controllers were designed without the luxury of using microprocessors, most modern systems use either a single microprocessor such as the 8086 or Z80, or multiple microprocessors such as the AMD 2903, usedin a bit slice architecture. Scan Techniques By definition and design, the programmable controller is dedicated to the continuous, repetitive task of examining the system inputs, solving the current control logic, and updating the system outputs. This task is referred to as scanning (sometimes called sweeping),and is acplished in slightly different ways in each manufacturer’s programmable controller. I/O Modules An I/O module is the entity within a puter responsible for the control of one or more external 35 devices and for the exchange of data between those devices and main memory and /or CPU registers. Thus, the I/O module must have and interface internal to the puter (to the CPU and main memory) and an interface external to the puter (to the external device). The major functions or requirements for an I/O module fall into the following categories: （ 1） Control and timing （ 2） CPU Communication （ 3） Device Communication （ 4） Data Buffering （ 5） Error Detection During any period of time, the CPU may municate with one or more external devices in unpredictable patterns, depending on the program’s need for I/O. The internal resources, such as main memory and the system buys, must be shared among a number of activities including data I/O. Thus, the I/O function includes a control and timing requirement, to coordinate the flow of traffic between internal resources and external devices. For example, the control of the transfer of data from an external device to the CPU might involve the following sequence of steps: 1） The CPU interrogates the I/O module to check the status of the attached device. 2） The I/O module returns the device status. 3） If the device is operational and ready to transmit, the CPU requests the transfer of data, by means of a mand to the I/O module. 4） The I/O module obtains a unit of data (., 8 or 16 bits) from the external device. The data are transferred from the I/O module to the CPU. If the system employs a bus, then each of the interactions between the CPU and the I/O module involves one or more bus arbitrations. The preceding simplified scenario also illustrates that the I/O module must have the capability to engage in munication with the CPU and with the external device. CPU munication involves: Command Decoding: The I/O module accepts mands from the CPU. These mands are generally sent as signals on the control bus. For example, an I/O module for a disk drive might accept the following mands: READ SECTOR, WRITE SECTOR, SEEK track number, and SCAN record ID. The latter two mands each include a parameter that is sent on the data bus . Data: Data are exchanged between the CPU and the I/O module over the data bus. Status Reporting: Because peripherals are so slow, it is important to know the status of the I/O module. For example, if an I/O module is asked to send data to the CPU (read), it may not be ready
。 break。 break。 break。 EX0=1。 alar_deal(0)。 break。 EX0=0。 igni_deal(0)。 switch(cond_teleamp。 igni_deal(0)。 for(。i++)。 for(i=0。 default:break。 case 1:igni_out=true。 32 } } void igni_deal(uchar i) {switch(i) { case 0:igni_out=false。 alar_out=false。 } else {alar_out=true。 alar_out=false。 if(j) while(i) { alar_out=true。 EX0=1。 igni_deal(0)。 } void service_int1()interrupt 2 using 1 {if(running==true) { running=false。 } EX0=0。 } void service_int0()interrupt 0 using 0 31 { if(running==false) { running=true。 cond_tele=0X00。 alar_out=0。 EX0=1。 //延時子程序 void system_init(void) {TCON=0X05。//報警處理程序 void igni_deal(uchar i)。 //外部中斷 0服務(wù)程序 void service_int1()。//點火器電路 void system_init(void)。//遙控關(guān)閉報警系統(tǒng) sbit alar_out=P2^6。 //裝置啟動或停止標志，為 true時啟動 sbit star_tele=P0^0。 27 附 錄 1主電路 12345678A B C D87654321DCBATitleNumberRevisionSizeA3Date:16Jun2008Sheet of File:E:\畢業(yè)設(shè)計2\汽車防盜報警\論文成文\原理圖.ddbDrawn By:GND+5