1、附录四 外文资料翻译 A microcontroller (or MCU) is a computer-on-a-chip. It is a type of microprocessor emphasizing self-sufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor (the kind used in a PC). The majority of computer systems in use today are embedded in other machinery, s
2、uch as telephones, clocks, appliances, vehicles, and infrastructure. An embedded system usually has minimal requirements for memory and program length and may require simple but unusual input/output systems. For example, most embedded systems lack keyboards, screens, disks, printers, or other recogn
3、izable I/O devices of a personal computer. They may control electric motors, relays or voltages, and read switches, variable resistors or other electronic devices. Often, the only I/O device readable by a human is a single light-emitting diode, and severe cost or power constraints can even eliminate
4、 that. In contrast to general-purpose CPUs, microcontrollers do not have an address bus or a data bus, because they integrate all the RAM and non-volatile memory on the same chip as the CPU. Because they need fewer pins, the chip can be placed in a much smaller, cheaper package. Integrating the memo
5、ry and other peripherals on a single chip and testing them as a unit increases the cost of that chip, but often results in decreased net cost of the embedded system as a whole. (Even if the cost of a CPU that has integrated peripherals is slightly more than the cost of a CPU + external peripherals,
6、having fewer chips typically allows a smaller and cheaper circuit board, and reduces the labor required to assemble and test the circuit board). This trend leads to design. A microcontroller is a single integrated circuit, commonly with the following features: central processing unit - ranging from
7、small and simple 4-bit processors to sophisticated 32- or 64-bit processors input/output interfaces such as serial ports (UARTs) other serial communications interfaces like IC, Serial Peripheral Interface and Controller Area Network for system interconnect peripherals such as timers and watchdog RAM
8、 for data storage ROM, EPROM, EEPROM or Flash memory for program storage clock generator - often an oscillator for a quartz timing crystal, resonator or RC circuit many include analog-to-digital converters This integration drastically reduces the number of chips and the amount of wiring and PCB spac
9、e that would be needed to produce equivalent systems using separate chips and have proved to be highly popular in embedded systems since their introduction in the 1970s. Some microcontrollers can afford to use a Harvard architecture: separate memory buses for instructions and data, allowing accesses
10、 to take place concurrently. The decision of which peripheral to integrate is often difficult. The Microcontroller vendors often trade operating frequencies and system design flexibility against time-to-market requirements from their customers and overall lower system cost. Manufacturers have to bal
11、ance the need to minimize the chip size against additional functionality. Microcontroller architectures are available from many different vendors in so many varieties that each instruction set architecture could rightly belong to a category of their own. Chief among these are the 8051, Z80 and ARM d
12、erivatives. Higher performance with the 80C51： Specifically targeted at high-end 8-bit microprocessor applications requiring low power consumption, the 80C51 has all of the 8051s architectural features, including its enhanced CPU and I/O functions. The on-chip program memory size remains 4 Kbytes, w
13、ith a full 64-kbyte external range. The 128byte on-chip RAM also is externally expandable to 64kbytes. Also , on board are two 16-bit time counters , a full duplex serial port, and a 1-bit Boolean processor for control functions, Figure 2b shows the 80C51s pinot for both the expanded and the port mo
14、de. The 80S52 has a Vcc range of 4 to 6 V and is TTL-compatible between 4.5-5.5V, above 4.5V, the chip operates at clock rates of up to 15 MHz (see the table). the 80S52 offers an idle mode for lower power dissipation .This mode is initiated by setting a bit in a new on-chip register, called the PCO
15、N register that resides in previously unused chip area. When the bit is set, the CPU is disabled, but the timer-counter, interrupts, and serial port continue to function normally. A reset or any enabled interrupt terminates the idle mode. If an interrupt ends the idle mode. all register data remain
16、unchanged and the interrupt is serviced. idle is implemented in much the same way as on the 80c49, that is, by splitting the on-chip clocks into two signals, one for the CPU and the other for the active idle circuitry, Using this technique, current drain in the idle mode is about 1 mA at a supply vo
17、ltage of 6 V and an operating frequency of 15 MHz Other bits of the PCON registers can be set as flags to determine whether an interrupt has been used for its normal function or to terminate the idle mode. These flags permit an interrupt to do double duty, instead of having to dedicate a particular
18、interrupt specifically to this mode. The AT89S2 is a low-power, high-performance CMOS 8-bit microcomputer with 8K 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-
19、standard MCS-51 instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcomputer which provides a
20、highly-flexible and cost-effective solution to many embedded control applications. The AT89S52 provides the following standard features:8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a six vector two-level interrupt architecture, a full duplex serial port, on-chip osci
21、llator and clock circuitry. In addition, the AT89S52 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
