1、附录 III 外文资料 英文文献 The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmels high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 ins
2、truction set and pinout. The on-chip Flash allows the program memory to be reprogrammed insystem or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highlyflexible and c
3、ost-effective solution to many embedded control applications. Features * Compatible with MCS-51 Products * 4K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000 Write/Erase Cycles * Fully Static Operation: 0 Hz to 24 MHz * Three-level Program Memory Lock * 128 x 8-bit Internal RAM * 32
4、Programmable I/O Lines * Two 16-bit Timer/Counters * Six Interrupt Sources * Programmable Serial Channel * Low-power Idle and Power-down Modes The AT89C51 provides the following standard features: 4Kbytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bittimer/counters, a five vector two-level int
5、errupt architecture,a full duplex serial port, on-chip oscillator and clock cir-cuitry. In addition, the AT89C51 is designed with static logicfor operation down to zero frequency and supports twosoftware selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counter
6、s,serial port and interrupt system to continue functioning. ThePower-down Mode saves the RAM contents but freezesthe oscillator disabling all other chip functions until the nexthardware reset. Pin Description VCC Supply voltage. GND Ground. Port 0 Port 0 is an 8-bit open-drain bi-directional I/O por
7、t. As anoutput port, each pin can sink eight TTL inputs. When 1sare written to port 0 pins, the pins can be used as high-impedance 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 internalpu
8、llups. Port 0 also receives the code bytes during Flash program- ming, and outputs the code bytes during programverification. External pullups are required during programverification. Port 1 Port 1 is an 8-bit bi-directional I/O port with internal pullups.The Port 1 output buffers can sink/source fo
9、ur TTL inputs.When 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 sourcecurrent (I ) because of the internal pullups. Port 1 also receives the low-order address bytes duringFlash pr
10、ogramming and verification. Port 2 Port 2 is an 8-bit bi-directional I/O port with internal pullups.ThePort 2 output buffers can sink/source four TTL inputs.When 1s are written to Port 2 pins they are pulled high bythe internal pullups and can be used as inputs. As inputs,Port 2 pins that are extern
11、ally being pulled low will sourcecurrent (I ) because of the internal pullups. Port 2 emits the high-order address byte during fetchesfrom external program memory and during accesses toexternal data memory that use 16-bit addresses (MOVX DPTR). In this application, it uses strong internal pullupswhe
12、n emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX RI), Port 2 emits thecontents of the P2 Special Function Register. Port 2 also receives the high-order address bits and somecontrol signals during Flash programming and verification. Port 3 Port 3 is an 8-bit bi-di
13、rectional I/O port with internal pullups.ThePort 3 output buffers can sink/source four TTL inputs.When 1s are written to Port 3 pins they are pulled high bythe internal pullups and can be used as inputs. As inputs,Port 3 pins that are externally being pulled low will sourcecurrent (I ) because of th
14、e pullups. Port 3 also serves the functions of various special features of the AT89C51 as listed below: Port Pin Alternate Functions P3.0 RXD (serial input port) P3.1 TXD (serial output port) P3.2 INT0 (external interrupt 0) P3.3 INT1 (external interrupt 1) P3.4 T0 (timer 0 external input) P3.5 T1 (
15、timer 1 external input) P3.6 WR (external data memory write strobe) P3.7 RD (external data memory read strobe) Port 3 also receives some control signals for Flash pro- gramming and verification. RST Reset input. A high on this pin for two machine cycles whilethe oscillator is running resets the device. ALE/PROG Address Latch Enable output pulse for latching the low byteof the address during accesses to external memory. Thispin is also the program pulse input (PROG) during
