SUMMARY
The various concepts and terms discussed in this chapter are summarized below:
Computer Structure
· Digital Computer-a programmable machine that processes binary data. It includes four components: CPU (ALU plus control unit), memory, input, and output.
· CPU-the Central Processing Unit. The group of circuits that processes data and provides control signals and timing. It includes the arithmetic/logic unit, registers, instruction decoder, and the control unit.
· ALU-the group of circuits that performs arithmetic and logic operations. The ALU is a part of the CPU.
· Control Unit-The group of circuits that provides timing and signals to all operations in the computer and controls data flow.
· Memory-a medium that stores binary information (instructions and data).
· Input -a device that transfers information from the outside world to the computer.
· Output-a device that transfers information from the computer to the outside world.
Scale of Integration
· SSI-Small-Scale Integration. The process of designing a few circuits on a single chip. The term refers to the technology used to fabricate discrete logic gates on a chip.
· MSI-Medium-Scalc Integration. The process of designing more than 100 gates on a single chip.
· LSI-Large-Scale Integration. The process of designing more than 1 ,000 gates on a single chip. Similarly, the terms VLSI (Very-Large-Scale Integration) and SLSI (Super-Large-Scale Integration) are used to indicate the scale of integration.
Microprocessor-Based Systems
· Microprocessor-a semiconductor device (integrated circuit) that is manufactured by using the large-scale integration technique. It includes the ALU, register arrays, and control circuits on a single chip.
· Microcomputer-a computer that uses a microprocessor as its CPU. It includes four components: microprocessor, memory, input, and output.
· Bus—a group of lines used to transfer bits between the microprocessor and other components of the computer system.
· ROM-Read-Only Memory. A memory that stores binary information permanently. The information can be read from this memory but cannot be altered.
· R/WM-Read/Write Memory. A memory that stores binary information during the operation of the computer. This memory is used as a writing pad to write user programs and data. The information stored in this memory can be easily read and altered.
Computer Languages
· Bit-A binary digit, 0 or 1.
· Byte-a group of eight bits.
· Nibble-a group of four bits.
· Word-a group of bits the computer recognizes and processes as a whole.
· Instruction-a command in binary that is recognized and executed by the computer in order to accomplish a task. Some instructions are designed with one word, and some require multiple words.
· Mnemonic-a combination of letters to suggest the operation of an instruction.
· Program-a set of instructions written in a specific sequence for the computer to accomplish a given task.
· Machine Language-the binary medium of communication with a computer through a designed set of instructions specific to each computer.
· Assembly Language-a medium of communication with a computer in which programs are written in mnemonics. An assembly language is specific to a given computer.
· Low-Level Language-a medium of communication that is machine-dependent, or specific to a given computer. The machine and the assembly languages of a computer are considered low-level languages. Programs written in these languages are not transferable to different types of machines.
· High-Level Language-a medium of communication independent of a given computer. Programs are written in English-like words, and they can be executed on a machine using a translator (a compiler or an interpreter).
· Compiler-a program that translates English-like words of a ‘high-level language into the machine language of a computer. A compiler reads a given program, called a source code, in its entirety, and then translates the program into the machine language, which is called an object code.
· Interpreter-a program that translates the English-like statements of a high level language into the machine language of a computer. An interpreter translates one statement at a time from a source code to an object code.
· Assembler-a computer program that translates an assembly language program from mnemonics to the binary machine code of a computer.
· Hand Assembly-a procedure of looking up the machine code manually from the instruction set of a microprocessor and entering those codes into the computer through a keyboard.
· Monitor Program-a program that interprets the input from a keyboard an converts the inputinto its binary equivalent.
LOOKING AHEAD
This chapter has given a brief introduction to computer organization and computer languages, with emphasis on the Z80 microprocessor and its assembly language. The chapter has given an overview of the entire spectrum of computers, including their salient features and applications. The primary focus ‘of this book is on the architectural details of the Z80 microprocessor and its industrial applications. and on assembly language programming in the context of these applications. In the microcomputer field, there is hardly any separation between hardware and software. especially in applications where assembly language is necessary. In designing a microprocessor-based product, hardware and software tasks are carried out concurrently because a decision in one area affects the planning of the other area. There are various functions that can be performed through either hardware or software. and a designer needs to consider both approaches. This book focuses on trade-off between the two approaches as a design philosophy.
ASSIGNMENTS
1. List the components of a microprocessor-based system or a computer.
2. Explain the functions of each component of a computer.
3. What is a microprocessor? What is the difference between a microprocessor and a CPU?
4. Explain the difference between a microprocessor and a microcomputer.
5. Explain the following terms: SSI. MSI. and LSI.
6. Define: bit. byte, word, and instruction.
7. How many bytes make a word of 32 bits?
8. Explain the difference between the machine language and the assembly language of the Z80 microprocessor.
9. What is an assembler?
10. What are low- and high-level languages?
11. Explain the difference between a compiler and an interpreter.
12. What are the advantages of an assembly language in comparison with high level languages?