外文文獻(xiàn)及翻譯--51單片機簡介-單片機-預(yù)覽頁
【正文】 ff, up to two machine cycles before the internal reset algorithm takes control. Onchip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory. Powerdown Mode In the powerdown mode, the oscillator is stopped, and the instruction that invokes powerdown is the last instruction executed. The onchip RAM and Special Function Registers retain their values until the powerdown mode is terminated. The only exit from powerdown is a hardware reset. Reset redefines the SFRs but does not change the onchip RAM. The reset should not be activated before VCC is restored to its normal operating level and must be held active long enough to allow the oscillator to restart and stabilize. Program Memory Lock Bits On the chip are three lock bits which can be left unprogrammed (U) or can be programmed (P) to obtain the additional features listed in the table below. When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched during reset. If the device is powered up without a reset, the latch initializes to a random value, and holds that value until reset is activated. It is necessary that the latched value of EA be in agreement with the current logic level at that pin in order for the device to function properly. 外文翻譯： 51單片機簡介 描述 AT89C51 是一個低電壓，高性能 CMOS8 位單片機帶有 4K 字節(jié)的可反復(fù)擦寫的程序存儲器（ PENROM）。 功能特性 AT89C51提供以下的功能標(biāo)準(zhǔn)： 4K 字節(jié)閃爍存儲器， 128 字節(jié)隨機存取數(shù)據(jù)存儲器， 32個 I/O 口， 2 個 16位定時 /計數(shù)器， 1 個 5向量兩級中斷結(jié)構(gòu)， 1個串行通信口，片內(nèi)震蕩器和時鐘電路。 引腳描述 VCC：電源電壓 GND：地 P0口： P0 口是一組 8 位漏極開路雙向 I/O 口，即地址 /數(shù)據(jù)總線復(fù)用口。 P0 口在閃爍編程時， P0 口接收指令，在程序校驗時，輸出指令，需要接電阻。閃爍編程時和程序校驗時， P1口接收低 8位地址。在訪問外部程序存儲器或 16位地址的外部數(shù)據(jù)存儲器時， P2 口送出高 8 位地址數(shù)據(jù)。對 P3 口寫如 “1”時，它們被內(nèi)部電阻拉到高電平并可作為輸入端時，被外部拉低的 P3口將用電阻輸出電流。 ALE/PROG： 當(dāng)訪問外部程序存儲器或數(shù)據(jù)存儲器時， ALE 輸出脈沖用于鎖存地址的低 8位字節(jié)。這個位置后只有一條 MOVX和 MOVC指令 ALE才會被應(yīng)用。 EA/VPP： 外部訪問允許。閃爍存儲器編程時，該引腳加上 +12V的編程允許電壓 VPP，當(dāng)然這必須是該器件是使用 12V編程電 壓 VPP。這個放大器與作為反饋元件的片外石英晶體或陶瓷諧振器一起構(gòu)成自然振蕩器。10PF，而如果使用陶瓷振蕩器建議選擇 40PF177。這種情況下，外部時鐘脈沖接到 XTAL1 端，即內(nèi)部時鐘發(fā)生器的輸入端， XTAL2則懸空。 PD是掉電模式，當(dāng) PD=1時，激活掉電工作模式，單片機進(jìn)入掉電工作狀態(tài)。此 時，片內(nèi)隨機存取數(shù)據(jù)存儲器和所有特殊功能寄存器的內(nèi)容保持不變。二是通過硬件復(fù)位也可將閑散工作模式終止。 閑散和掉電模式外部引 腳
畢業(yè)設(shè)計相關(guān)推薦
鄂ICP備17016276號-1