【文章內(nèi)容簡介】 ble and costeffective solution to many embedded control applications. The AT89C2051 provides the following standard features: 2K bytes of Flash, 128 bytes of RAM, 15 I/O lines, two 16bit timer/counters, a five vector twolevel interrupt architecture, a full duplex serial port, a precision analog parator, onchip oscillator and clock circuitry. In addition, the AT89C2051 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 powerdown mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset. 8bit Microcontroller with 2K Bytes Flash AT89C2051 0368HPin Configurations Block Diagram Pin Description VCC Supply voltage. GND Ground. Port 0 Port 0 is an 8bit opendrain bidirectional I/O port. As anoutput port, each pin can sink eight TTL inputs. When 1sare written to port 0 pins, the pins can be used as highimpedanceinputs. Port 0 may also be configured to be the multiplexed loworderaddress/data bus during accesses to external programand data memory. In this mode P0 has internalpullups. Port 0 also receives the code bytes during Flash programming,and outputs the code bytes during programverification. 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 (IIL) because of the internal 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 (IIL) because of the internal 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 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 (IIL) because of the 3 also serves the functions of various special features of the AT89C2051 as listed below: Port PinAlternateFunctions RXD(serialinputport) TXD(serialoutputport) INT0(externalinterrupt0) INT1(externalinterrupt1) T0(timer0externalinput) T1(timer1externalinput) Port 3 also receives some control signals for Flash programming and verification. 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 normal operation ALE is emitted at a constant rate of 1/6the 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 Dat