【正文】
onechip puter series which Intel Company produces. This pany introduced 8 topgrade onechip puters of MCS51 series in 1980 after introducing 8 onechip puters of MCS48 series in 1976. It belong to a lot of kinds this line of onechip puter the chips have,such as 8051, 8031, 8751, 80C51BH, 80C31BH,etc., their basic position, basic performance and instruction system are all the same. 8051 daily representatives 51 serial onechip puters . An onechip puter system is made up of several following parts: ( 1) One microprocessor of 8 (CPU). ( 2) At slice data memory RAM (128B/256B),it use not depositting not can reading /data that write, such as result not middle of operation, final result and data wanted to show, etc. ( 3) Procedure memory ROM/EPROM (4KB/8KB ), is used to preserve the procedure , some initial data and form in slice. But does not take ROM/EPROM within some onechip puters, such as 8031 , 8032, 80C ,etc.. ( 4) Four 8 run side by side I/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 The circuit of 8051 onechip puters and four I/O ports is very ingenious in design. Familiar with I/O port logical circuit, not only help to use ports correctly and rationally, and will inspire to designing the peripheral logical circuit of onechip puter to some extent. Load ability and interface of port have certain requirement, because output grade, P0 of mouth and P1 end output, P3 of mouth grade different at structure, so, the load ability and interface of its door demand to have nothing in mon with each other. P0 mouth is different from other mouths, its output grade draws the resistance supremly. When using it as the mouth in mon use to use, output grade is it leak circuit to turn on, is it is it urge NMOS draw the resistance on taking to be outer with it while inputting to go out to fail. When being used as introduction, should write 1 to a latch first. Every one with P0 mouth can drive 8 Model LS TTL load to export. P1 mouth is an accurate twoway mouth too, used as I/O in mon use. Different from P0 mouth output of circuit its, draw load resistance link with power on inside have. In fact, the resistance is that two effects are in charge of FET and together