serial communication interface motorola 68hc11

The cache memoryhas a copy of the most recently accessed instructions and data.

If you continue browsing the site, you agree to the use of cookies on this website.

The computer hard-ware consists of four main components: (1) a processor, which serves as thecomputers brain, (2) an input unit, through which programs and data canbe entered into the computer, (3) an output unit, on which computationalresults can be displayed, and (4) memory, in which the computer softwareprograms and data are stored.

Figure 1.1 shows a simple block diagram of acomputer.

The processor communicates with memory and inputoutput(IO) devices through a set of signal lines referred to as a bus.

The commonbus actually consists of three buses: a data bus, an address bus, and a con-trol bus.1.2.1 The ProcessorThe processor, which is also called the central processing unit (CPU), canbe further divided into three major parts:Registers.

It is used to holddata andor a memory address during execution of an instruction.

Access todata in registers is faster than access to data in memory.

Registers play anessential role in the efficient execution of programs.

The number of registersvaries greatly from computer to computer.Arithmetic logic unit.

The arithmetic logic unit (ALU) is the computersnumerical calculator and logical operation evaluator.

The ALU receives datafrom main memory andor registers, performs a computation, and, if neces-sary, writes the result back to main memory or registers.

Todays fastest per-sonal computer can perform hundreds of millions of additions in one second.Control unit.

The control unit contains the hardware instruction logic.The control unit decodes and monitors the execution of instructions.

The con-trol unit also acts as an arbiter as various portions of the computer systemcompete for the resources of the CPU.

The activities of the CPU are synchro-nized by the system clock.

The control unitalso maintains a register called a program counter (PC), which controls thememory address of the next instruction to be executed.

During the executionof an instruction, the presence of overflow, an addition carry, a subtractionborrow, and so forth, are flagged by the system and stored in another registercalled a status register.

The resultant flags are then used by the programmerfor program control and decision-making.2 Chapter 1 I Introduction to Motorola 68HC11HUANG Ch01001-036 32800 12:38 PM Page 2.

A microprocessor is a processor packaged in a single integratedcircuit.

A microcomputer is a computer that uses a microprocessor as its CPU.Early microcomputers are quite simple and slow.

However, many of todaysdesktop microcomputers have become very sophisticated and are even fasterthan many large computers manufactured only a few years ago.Microprocessors come in 4-bit, 8-bit, 16-bit, 32-bit, and 64-bit models.

Thenumber of bits refers to the number of binary digits that the microprocessorcan manipulate in one operation.

A 4-bit microprocessor, for example, is capa-ble of manipulating 4 bits of information in one operation.

Four-bit micro-processors are used for the electronic control of relatively simple machines.Some pocket calculators, for example, contain 4-bit microprocessors.The access of main memory takes much longer than the period of the CPUcontrol clock signal.

To enhance the CPU performance, many 32-bit and 64-bitmicroprocessors contain on-chip high-speed cache memory.

Serial Communication Interface Motorola 68Hc11