外文原文
A: Fundamentals of Single-chip Microcomputer中国特色社会主义文化
The single-chip microcomputer is the culmination of both the development of the digital computer and the integrated circuit arguably the tow most significant inventions of the 20th century 空气炸锅怎么炸薯条
The tow types of architecture are found in single-chip microcomputer. Some employ the split program/data memory of the Harvard architecture, shown in Fig.3-5A-1, others follow the philosophy, widely adapted for general-purpo computers and microprocessors, of making no logical distinction between program and data memory as in the Princeton architecture, shown in Fig.3-5A-2.
听了会开心的歌In general terms a single-chip microcomputer is characterized by the incorporation of all the units of a computer into a single device, as shown in Fig3-5A-3.
Fig.3-5A-1 A Harvard type
Fig.3-5A-2. A conventional Princeton computer
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Fig3-5A-3. Principal features of a microcomputer
Read only memory (ROM)
ROM is usually for the permanent, non-volatile storage of an applications program .Many microcomputers and microcontrollers are intended for high-volume applications and hence the economical manufacture of the devices requires that the contents of the program memory be committed permanently during the manufacture of chips . Clearly, this implies a rigorous approach to ROM code development since changes cannot be made after manufacture .This development process may involve emulation using a sophi
sticated development system with a hardware emulation capability as well as the u of powerful software tools.
Some manufacturers provide additional ROM options by including in their range devices with (or intended for u with) ur programmable memory. The simplest of the is usually device which can operate in a microprocessor mode by using some of the input/output lines as an address and data bus for accessing external memory. This type of device can behave functionally as the single chip microcomputer from which it is derived albeit with restricted I/O and a modified external circuit. The u of the ROM less devices is common even in production circuits where the volume does not justify the development costs of custom on-chip ROM[2];there can still be a significant saving in I/O and other chips compared to a conventional microprocessor bad circuit. More exact replacement for ROM devices can be obtained in the form of variants with 'piggy-back' EPROM(Erasable programmable ROM )sockets or devices with EPROM instead of ROM 择天记黑袍。The devices are naturally more expensive than equivalent ROM device, but do provide complete circuit equivalents. EPROM bad devices are also extremely attractive
for low-volume applications where they provide the advantages of a single-chip device, in terms of on-chip I/O, etc. ,with the convenience of flexible ur programmability.
Random access memory (RAM).
RAM is for the storage of working variables and data ud during program execution. The size of this memory varies with device type but it has the same characteristic width (4,8,16 bits etc.) as the processor ,Special function registers, such as stack pointer or timer register are often logically incorporated into the RAM area. It is also common in Hard type microcomputers to treat the RAM area as a collection of register; it is unnecessary to make distinction between RAM and processor register as is done in the ca of a microprocessor system since RAM and registers are not usually physically parated in a microcomputer .
Central processing unit (CPU).如何推广新媒体平台The CPU is much like that of any microprocessor. Many applications of microcomputers and microcontrollers involve the handling of binary-coded decimal (BCD) data (for numerical displays, for example) ,hence it is common to find that
the CPU is well adapted to handling this type of data .It is also common to find good facilities for testing, tting and retting individual bits of memory or I/O since many controller applications involve the turning on and off of single output lines or the reading the single line. The lines are readily interfaced to two-state devices such as switches, thermostats, solid-state relays, valves, motor, etc.
Parallel input/output.
Parallel input and output schemes vary somewhat in different microcomputer; in most a mechanism is provided to at least allow some flexibility of choosing which pins are outputs and which are inputs. This may apply to all or some of the ports. Some I/O lines are suitable for direct interfacing to, for example, fluorescent displays, or can provide sufficient current to make interfacing other components straightforward. Some devices allow an I/O port to be configured as a system bus to allow off-chip memory and I/O expansion. This facility is potentially uful as a product range develops, since successive enhancements may become too big for on-chip memory and it is undesirable not to build on the existing software ba.
Serial input/output .
Serial communication with terminal devices is common means of providing a link using a small number of lines. This sort of communication can also be exploited for interfacing special function chips or linking veral microcomputers together .Both the common asynchronous synchronous communication schemes require protocols that provide framing (start and stop) information .This can be implemented as a hardware facility or U(S)电脑黑屏开不了机 ART(Universal(synchronous) asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this low-level, time-consuming, detail. t is merely necessary to lected a baud-rate and possibly other options (number of stop bits, parity, etc.) and load (or read from) the rial transmitter (or receiver) buffer. Serialization of the data in the appropriate format is then handled by the hardware circuit.
