【正文】 O interface P0 four P3, each mouth can use as introduction , may use as exporting too. ( 5) Two timer / counter, each timer / counter may set up and count in the way, used to count to the external incident, can set up into a timing way too, and can according to count or result of timing realize the control of the puter. ( 6) Five cut off cutting off the control system of the source . ( 7) One all duplexing serial I/O mouth of UART (universal asynchronous receiver/transmitter (UART) ), is it realize onechip puter or onechip puter and serial munication of puter to use for. ( 8) Stretch oscillator and clock produce circuit, quartz crystal finely tune electric capacity need outer. Allow oscillation frequency as 12 megahertas now at most. Every the abovementioned part was joined through the inside data bus .Among them, CPU is a core of the onechip puter, it is the control of the puter and mand centre, made up of such parts as arithmetic unit and controller , etc.. The arithmetic unit can carry on 8 persons of arithmetic operation and unit ALU of logic operation while including one, the 1 storing device temporarilies of 8, storing device 2 temporarily, 839。 P0 mouth is a twoway bus, send the introduction of 8 low addresses and data / export in timesharing Output grade , P3 of mouth , P1 of P1 , connect with inside have load resistance of drawing , every one of they can drive 4 Model LS TTL load to output. As while inputting the mouth, any TTL or NMOS circuit can drive P1 of 8051 onechip puters as P3 mouth in a normal way . Because draw resistance on output grade of them have, can open a way collector too or drainsource resistance is it urge to open a way, do not need to have the resistance of drawing outerly . Mouths are all accurate twoway mouths too. When the conduct is input, must write the corresponding port latch with 1 first . As to 80C51 onechip puter, port can only offer milliampere of output electric currents, is it output mouth go when urging one ordinary basing of transistor to regard as, should contact a resistance among the port and transistor base , in order to the electricity while restraining the high level from exporting P1~P3 Being restored to the throne is the operation of initializing of an onechip puter. Its main function is to turn PC into 0000H initially , make the onechip puter begin to hold the conduct procedure from unit 0000H. Except that the ones that enter the system are initialized normally,as because procedure operate it make mistakes or operate there aren39。s trigger, restore to the throne circuit sample to output , Schmitt of trigger constantly in each S5P2 , machine of cycle in having one more , then just got and restored to the throne and operated the necessary signal insidly. Restore to the throne resistance of circuit generally, electric capacity parameter suitable for 6 brilliant to shake, can is it restore to the throne signal high level duration greater than 2 machine cycles to guarantee. Being restored to the throne in the circuit is simple, its function is very important. Pieces of onechip puter system could normal running,should first check it can restore to the throne not succeeding. Checking and can pop on