AT89C2051AT89C2051 is made in the ATMEL Corporation, which is the low-voltage, high-performance CMOS8-bit microcontroller,Tablets containing repeated 2k bytes of program memory erasable read-only (PEROM) and random 128bytes data memory (RAM), device using ATMELs high density, non-volatile memory technology, Compatible with the standard of MCS-51 instruction set, built-chip 8-bit general-purpose central processing unit and repeatedly write the Flash memory, which can effectively reduce the development costs. AT89C2051 features a powerful single-chip can provide cost-effective in many Applications.Main features:Compatible the MCS51 command system;Contains the 2KB memory re-programming FLASH (1000);2.7 6V voltage range;the whole Static work: 0Hz 24KHz;Secrets 2 Program Memory Lock128 8-bit internal RAM15 programmable I / O linesTwo 16-bit timer / counter6 interrupt sources, two external interrupt sourcesProgrammable Serial ChannelHigh Precision Voltage Comparator （P1.0，P1.1，P3.6）；Have the output port of the LED direct drive Low-power idle and power-down mode The pin Picture of AT89C2051Picture one the pin of AT89C2051AT89C2051s functional description:VCC: Power Supply VoltageGND: landP1 port: P1 mouth is a group of 8-bit bi-directional I / O interface, P1.2 P1.7 provide internal pull-up resistor,P1.0 and P1.1 internal supreme pull-up resistor. P1 mouth output buffer can absorb the current 20mA and direct-drive LED.When Programming and calibration, P1 mouth as the eighth address receive.P3 mouth: P3 port P3.0 P3.5, P3.7 is the internal pull-up resistor with the seven bi-directional I / O interface. Did not bring out the P3.6，It as a generic I / O port, but can not visit. Can be used as a fixed-chip input comparator output signal. when P3 write 1, they were highed the internal pull-up resistor can be raised as an input port.P3 port special function as shown in table 1:Table 1 P3 mouths special features引脚功能特性P3.0RXD （串行输入口)P3.1TXD （串行输出口）P3.2 (外中断0)P3.3 (外中断1)P3.4T0 (定时/计数器0外部输入)P3.5T1 （定时/计数器1外部输入）RST：Reset output. When the oscillator device reset, RST pin to maintain the high level of two machine cycle time.XTAL1: the RP-oscillator amplifier and internal clock generator input.XTAL2: RP-oscillator output amplifier.TimerOverview of the Timer 89C2051 single-chip-chip has two 16-bit timer / counter, That is the timer 0 (T0) and Timer 1 (T1). They all have from time to time and event count function, Can be used for timing control, delay of external events, such as counting and testing occasions. Timers T0 and T1 two 16-bit timers in fact is 16-bit counter plus 1. Among them, T0 compositioned by the two 8-bit special function registers TH0 and TL0; T1 posed by the TH1 and TL1. These functions were controled by the special function registers TMOD and TCON When set to the work in the timing, Through the pin count of the external pulse signal. When the input pulse signal generated by the falling edge of 1-0, The value of timer plus 1. At of every machine cycle during the S5P2 sampling pin T0 and T1 the input level, if a machine cycle before sample value of 1, The next machine cycle sampling value is 0, The counter plus 1. Since then during S3P1 of the machine cycle, New value will into the counter.so Detection of a 1-0 transition of the two machine cycles,So The maximum count frequency of oscillation frequency of 1 / 24. In addition to the option of work from time to time or count,Each timer / counter have four kinds of work mode, That is, each of timer circuit kinds of four constitute a structural modelTwo low-power modeIdle modeIn idle mode, CPU to maintain sleep and all-chip peripherals remain active, this way generated in Software, At this point, Chip RAM and all the contents of special function registers remain unchanged. Idle mode was terminated by any interrupt request permission to or hardware reset.P1.0 and P1.1 ,in the non-use of external pull-up resistor on the case should be set to 0, Or in the use of pull-up resistor is set to 1.It should be noted that: when uses of hardware reset Termination idle mode, AT89C2051 is usually stopped from the program until the internal reset control of the two machine cycles before the restore procedure Service. In this case the hardware within the prohibition of the reading and writing of internal RAM, However, to allow access to ports, To eliminate the Hardware reset in the idle mode of port accidents may write, In principle, to enter the idle mode of instruction should not be under the command of a pin or an external memory port for a visit.Power-down modeIn power-down mode, the oscillator to stop working, enter the power-down mode ,Instructions, who was the last one, the implementation of the Directive, Chip RAM and all the contents of special function registers the termination of the previous power-down mode be frozen.