【正文】 gh voltage to low voltage ). 2 with stability, So, it has Sensitive layer of MQ7 gas sensitive ponents is made of SnO excellent long term stability. Its service life can reach 5 years under using condition. SENSITVITY ADJUSTMENT Resistance value of MQ7 is difference to various kinds and various concentration gases. So, When using this ponents, sensitivity adjustment is very necessary. we remend that you calibrate the detector for 200ppm CO in air and use value of Load resistance . When accurately measuring, the proper alarm point for the gas detector should be determined after considering the temperature and humidity influence. The sensitivity adjusting program: a. Connect the sensor to the application circuit. b. Turn on the power, keep preheating through electricity over 48 hours. c. Adjust the another load resistance RL until you get a signal value which is respond to a CO concentration at the end point of 60 seconds . AT89C51 The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16bit timer/counters, a five vector twolevel interrupt architecture, a full duplex serial port, onchip oscillator and clock circuitry. In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters,serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset. Pin Description V CC： Supply voltage. GND： round. Port 0： Port 0 is an 8bit open drain bidirectional I/O port. As an output port each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as highimpedance inputs. Port 0 may also be configured to be the multiplexed loworder address/data bus during accesses to external program and data memory. In this mode P0 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 Port 1 output buffers can sink/source four TTL 1s are written to Port 1 pins they are pulled high bythe internal pullups and can be used as inputs. As inputs,Port 1 pins that are externally being pulled low will source current (I IL) because of the internal pullups. 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 Port 2 output buffers can sink/source four TTL 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 (I IL) 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 use 16bit addresses (MOVX DPTR). In this application it 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. 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 Port 3 output buffers can sink/source four TTL 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 (I IL) because of the pullups. 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 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. PSEN： Program Store Enable is the read strobe to external program memory. When the AT89C51 is executing code from external pro gram memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory. EA /V PP： 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 0000H up to , however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to V CC for internal program executions. This pin also receives the 12volt programming enable volt age (V PP ) during Flash programming, for parts that V PP XTAL1： Input to the inverting oscillator amplifier and input to the internal clock operating circuit. XTAL2： Output from the inverting oscillator amplifier. 湖州師范學院求真學院本科畢業(yè)設(shè)計（論文）中期報告 學院 求真學院 班級 040832 學生姓名 潘泓旭 指導(dǎo)教師 陳建清 課題名稱 氣敏傳感檢測報警系統(tǒng) 預(yù)期成果形式 硬