1. Lecture on Microcomputer
Presented By

2. What is Microcomputer?

3. Typical Microcomputer Architecture

4. The Microcomputer Bus Address Bus
Information transfer one direction, microprocessor to memory or I/O elements, so unidirectional bus
Typically 20 to 32 bit long
Determines addressable memory, 1 MB to 4 GB

5. The Microcomputer Bus Data Bus Control Bus
Bidirectional i.e. to or from microprocessor
Multiplexed / time shared data bus e.g. in bit address is send through 16-bit data bus and 4 status lines
Determines the word size of the microcomputer
Control Bus
Used to send control signals to synchronize the operation of individual microcomputer elements
Each microcomputer has a unique set of control signals.

6. Clock Signals Clock generator generates clock signals
Most MPs have external clock generator circuit
Each instruction requires a number of clock signals
Clock signals determines the speed of MPs
The short period cycle means clock speed is large, means high speed of computer

7. The single chip microprocessor
Microprocessor is the CPU of the microcomputer
The main areas of microprocessor
Register section
The control unit
The arithmetic and logic unit (ALU)

8. Basic Microprocessor Registers
Instruction Register (IR): stores instructions
Program Counter (PC): contains the address of the next instruction to be executed
Memory Address Register (MAR): contains address of data
Accumulator (A): typically a 8 bit register, used to store result after most ALU operations

9. Accumulator based vs. general purpose based microprocessor
Intel 8085 and Motorola 6809 are accumulator based.
Accumulator is used as one of the data source
Result goes to accumulator
Example: ADD R1
General purpose based
Intel 8066/../Pentium are of this kind.
The registers contain hold data, memory address, results of ALU so on.
Example: ADD AX, BX, ADD [AX], BX

10. Use of the Basic Microprocessor Registers
Let us add contents of two memory locations
For example, add [2010] = 0002 and [2012] = 005
In general [NNNN] represents the content of the memory location NNNN.

11. Steps of Addition of [2010]+[2012]
Load MAR with 2010
Move contents of 2010 into data register, D0, which may be AX/BX etc.
Increment MAR by 2 to hold 2012
Add D0 with [2012] and store the result into D0
Instruction set form Motorola 68000

12. L E PC L E L E E L

13. Microprogramming the Control Unit
Each instruction is executed by a set of microinstructions
The microinstructions has their own codes
The codes are stored into internal memory, called the control memory (ROM)
Let us increment a register by 1

19. Assembly Language Instruction Format
Three address
Two address
One address
Zero address
CLD ; clear direction
NOP ; No operation
For all microprocessors