【正文】 else TR2 1 英文資料 Overview The 8051 family of micro controllers is based on an architecture which is highly optimized for embedded control systems It is used in a wide variety of applications from military equipment to automobiles to the keyboard on your PC Second only to the Motorola 68HC11 in eight bit processors sales the 8051 family of microcontrollers is available in a wide array of variations from manufacturers such as Intel Philips and Siemens These manufacturers have added numerous features and peripherals to the 8051 such as I2C interfaces analog to digital converters watchdog timers and pulse width modulated outputs Variations of the 8051 with clock speeds up to 40MHz and voltage requirements down to 15 volts are available This wide range of parts based on one core makes the 8051 family an excellent choice as the base architecture for a panys entire line of products since it can perform many functions and developers will only have to learn this one platform The basic architecture consists of the following features 1an eight bit ALU 232 descrete IO pins 4 groups of 8 which can be individually accessed 3two 16 bit timercounters 4full duplex UART 56 interrupt sources with 2 priority levels 6128 bytes of on board RAM 7separate 64K byte address spaces for DATA and CODE memory One 8051 processor cycle consists of twelve oscillator periods Each of the twelve oscillator periods is used for a special function by the 8051 core such as op code fetches and samples of the interrupt daisy chain for pending interrupts The time required for any 8051 instruction can be puted by dividing the clock frequency by 12 inverting that result and multiplying it by the number of processor cycles required by the instruction in question Therefore if you have a system which is using an 11059MHz clock you can pute the number of instructions per second by dividing this value by 12 This gives an instruction frequency of 921583 instructions per second Inverting this will provide the amount of time taken by each instruction cycle 1085 microseconds OnBoard TimerCounters The standard 8051 has two timercounters other 8051 family members have varying amounts each of which is a full 16 bits Each timercounter can be function as a free running timer in which case they count processor cycles or can be used to count falling edges on the signal applied to their respective IO pin either T0 or T1 When used as a counter the input signal must have a frequency equal to or lower than the instruction cycle frequency divided by 2 ie the oscillator frequency 24 since the ining signal is sampled every instruction cycle and the counter is incremented only when a 1 to 0 transition is detected which will require two samples If desired the timercounters can force a software interrupt when they overflow The TCON Timer Control SFR is used to start or stop the timers as well as hold the overflow flags of the timers The TCON SFR is detailed below in Table A 7 The timercounters are started or stopped by changing the timer run bits TR0 and TR1 in TCON The software can freeze the operation of either timer as well as restart the timers simply by changing the Trx bit in the TCON register The TCON register also contains the overflow flags for the timers When the timers overflow they set their respective flag TF0 or TF1 in this register When the processor detects a 0 to 1 transition in the flag an interrupt occurs if it is enabled It should be noted that the software can set or clear this flag at any time Therefore an interrupt can be prevented as well as forced by the software Microputer interface A microputer interface converts information between two forms Outside the microputer the information handled by an electronic system exists as a physical signals but within the program it is represented numerically The function of any interface can be broken down into a number of operations which modify the data in some way so than the process of conversion between the external and internal forms is carried out in a number or steps This can be illustrated by means of an example such as than or Fig 101which shows an interface between a microputer and a transducer producing a continuously variable analog signal transducers often produce very small out requiring amply frication or they may generate signals in a form that needs to be converted again before being handled by the rest of the system For example many transducers these variable resistance which must be converted to a voltage by a special circuit This process of converting the transducer output into a voltage4 signal which can be connected to the rest of the system is called signal conditioning In the example of Figure 101 the sigma conditioning section translates the range lf voltage or current signals from the transducer to one which can be converted to digital forum by an analogtodigital converter Fig 101 output Interface Analogtodigital – digital converter ADC is used to convert a continuously variable signal to a corresponding digital forum which can take any one of a fixed number of possible binary values If the output lf the transducer does not vary continuously no ADC is necessary In this case the signal conditioning section must convert the ining signal to a form which can be connected directly to the next part of the interface the inputoutput section lf the microputer itself The IO section convert