at89c51的介紹外文翻譯-其他專業(yè)-文庫(kù)吧
2024-12-30 06:19 本頁(yè)面
【正文】 s can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the internal Pullup resistors and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal Pullup resistors. Port 1 also receives the loworder address bytes during Flash programming and verification. Port 2 Port 2 is an 8bit bidirectional I/O port with internal Pullup resistor. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal Pullup resistor and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current, because of the internal Pullup resistor. Port 2 emits the highorder address byte during fetches from external program memory and during accesses to external data memory that use 16bit addresses. In this application, it uses strong internal Pullup resistor when emitting 1s. During accesses to external data memory that use 8bit addresses, Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the highorder address bits and some control signals during Flash programming and verification. 2021屆電子信息科學(xué)與技術(shù)專業(yè)畢業(yè)設(shè)計(jì)外文翻 譯 3 Port 3 Port 3 is an 8bit bidirectional I/O port with internal Pullup resistor. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal Pullup resistor and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the Pullup resistor. Port 3 also serves the functions of various special features of the AT89C51 as listed below: Port 3 also receives some control signals for Flash programming and verification. RST Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device. ALE/PROG Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit 2021屆電子信息科學(xué)與技術(shù)專業(yè)畢業(yè)設(shè)計(jì)外文翻 譯 4 set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALEdisable bit h
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