【導(dǎo)讀】等外部接口芯片器件的應(yīng)用。掉電保護(hù)功能；實現(xiàn)對單價的調(diào)整。按模擬傳感器信號的按鍵，顯示行駛里程與總金額。在軟件中實現(xiàn)起步價，單價。數(shù)碼管顯示起步里程、單價，總里程、總金額。設(shè)計的主要內(nèi)容是利用51單片機實現(xiàn)出租車計價器的功能。的控制也是相對容易，易于實現(xiàn)的。數(shù)碼管顯示的穩(wěn)定性雖不及液晶屏，但其價格比液晶屏便宜，由于本。設(shè)計簡單，采用數(shù)碼管顯示較好。選用存儲器芯片AT24C02組成掉電保護(hù)電路。AT89S51單片機芯片采用40引腳的雙列直插封裝方式。AT24C02是一個CMOS標(biāo)準(zhǔn)的EEPROM存儲器，掉電時能保存數(shù)據(jù)。需付總金額；按下清零按鍵，數(shù)碼管全顯示零，以備下次計價。現(xiàn)在各大中城市出租車行業(yè)都已普及自動計價器，所以計價器技術(shù)的發(fā)展已成定局。程計費求得客戶用車的總費用，并通過數(shù)碼管顯示相應(yīng)的里程及金額。我在本次設(shè)計中主要負(fù)責(zé)硬件工作。本電路以AT89S51單片機為中心，附加A44E霍。模擬出租車計價器設(shè)計：進(jìn)行里程顯示，預(yù)設(shè)起步價和起步公里數(shù)；行程按全程收費，

　　

【正文】 puts. When 1s are written to port 0 pins, the pins can be used as highimpedance inputs. Port 0 can also be configured to be the multiplexed loworder address/data bus during accesses to external program and data memory. In this mode, PO has internal pullups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes during program verification. External pullups are required during program verification. Port 1： Port 1 is an 8bit bidirectional I/O port with internal pullups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (lip) because of the internal pullups. Port 2： Port 2 is an 8bit bidirectional I/O port with internal pullups. 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 pullups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (lip) because of the internal pullups. Port 2 emits the highorder address byte during fetches from external program memory and during accesses to external data memory that uses 16bit addresses (MOVX@DPTR). In this application, Port 2 uses strong internal pullups when emitting 1s. During accesses to external data memory that use 8bit addresses (MOVX@RI), Port 2 emits the contents of the P2 Special Function Register. 畢業(yè)設(shè)計 第 頁 23 Port 2 also receives the highorder address bits and some control signals during Flash programming and verification. Port 3： Port 3 is an 8bit bidirectional I/O port with internal pullups. 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 pullups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (lip) because of the pullups. Port 3 receives some control signals for Flash programming and verification. Port 3 also serves the functions of various special features of the AT89S51， as shown in the following table. RST： Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device. This pin drives High for 98 oscillator periods after the Watchdog times out. The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit DISRTO, the RESET HIGH out feature is enabled. ALE/PROG： Address Latch Enable (ALE) is an 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 set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALEdisable bit has no effect if the microcontroller is in external execution mode. 畢業(yè)設(shè)計 第 頁 24 PSEN： Program Store Enable (PSEN) is the read strobe to external program memory. When the AT89S51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory. EA/VPP： External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at OOOOH up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to Vcc for internal program executions. This pin also receives the 12volt programming enable voltage (VPP) during Flash programming. XTAL1： Input to the inverting oscillator amplifier and input to the internal clock operating circuit. XTAL2： Output from the inverting oscillator amplifier Special Function Registers： Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect. User software should not write 1 s to these unlisted locations, since they may be used in future products to invoke new features. In that case, the reset or inactive values of the new bits will always be 0. Interrupt Registers: The individual interrupt enable bits are in the IE register. Two priorities can be set for each of the five interrupt sources in the IP register. 畢業(yè)設(shè)計 第 頁 25 Dual Data Pointer Registers: To facilitate accessing both internal and external data memory, two banks of 16bit Data Pointer Registers are provided: DPO at SFR address locations 82H83H and DP1 at DPS=0 in SFR AUXR1 selects DPO and DPS=1 selects DP1. The user should ALWAYS initialize the DPS bit to the appropriate value before accessing the respective Data Pointer Register. Power Off Flag: The Power Off Flag (POF) is located at bit 4 () in the PCON SFR. POF is set to 1”during power up. It can be set and rest under software control and is not affected by reset. Memory Organization： MCS51 devices have a separate address space for Program and Data Memory. Up to 64K bytes each of external Program and Data Memory can be addressed. Program Memory： If the EA pin is connected to G