电气电子专业外文翻译--at89c51的介绍-电气类(编辑修改稿)

电气电子专业外文翻译--at89c51的介绍-电气类(编辑修改稿)内容摘要：

pped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on should be strapped to VCC for internal program pin also receives the 12volt programming enable voltage(VPP) during Flash programming, for parts that require12volt VPP. XTAL1 Input to the inverting oscillator amplifier and input to the internal clock operating circuit. XTAL2 Output from the inverting oscillator amplifier. 13 Oscillator Characteristics XTAL1 and XTAL2 are the input and output, respectively,of an inverting amplifier which can be configured for use as an onchip oscillator, as shown in Figure a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a dividebytwo flipflop, but minimum and maximum voltage high and low time specifications must be observed. Figure 1. Oscillator Connections Figure 2. External Clock Drive Configuration Idle Mode In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The mode is invoked by software. The content of the onchip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware should be noted that when idle is terminated by a hard ware reset, the device normally resumes program execution,from where it left off, 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, 14 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 fr。