Microprocessor Architecture and its Operation: Lecture Notes, Lecture notes of Basic Electronics

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Microprocessor

Lecture 16

Microprocessor Architecture and its Operation

Microprocessor Architecture and it's Operation

Computer system consist primary of :-

1- Microprocessor.

2- Memory.

3- Input.

4- Output.

The internal logic design of the microprocessor called its "architecture", determine how and what various operations are performed by "Mp".

* Microprocessor architecture and its operations:-

The microprocessor is programmable logic device designed with register, flip-flop and timing elements.

All function performed by microprocessor can by classified

in three general categories:-

1- Microprocessor initiated operations.

2- Internal data operations.

3- Peripheral (or externally) initiated operations.

To performed these operations, microprocessor needs [logic circuit and control signals].

1- Mp Initiated Operations:-

Primarily microprocessor performs four operations:-

a) Memory read (Reads data from memory). b) Memory writes (Write data into memory). c) I/O read (Accept data to output device). d) I/O writes (Sends data to output device).

Figure (1). The 8085 bus structure.

To communication with a memory, for example to read

instruction from memory location:-

1- Mp placed 16-bit address on address bus.

2- The address on the bus is decoded by an external logic circuit.

3- The memory location is identified.

4- The Mp sends a pulse called memory read as control signal.

5- The pulse activates the memory chip.

6- The contents of the memory location (8-bit data) are placed on the data bus as in fig. (2).

D 7

A 15 A 0

MPU

D 0

Memory Input Output

Address bus

Data bus

Control bus

Memory Chip

Data bus

Memory read

Figure (2). Memory read operation

2- Internal Data Operations:-

The internal architecture of the 8085/8080A microprocessor determines hoe and what operation can be performed with the data. These operations are:- 1- Store 8-bit data. 2- Performed arithmetic and logical operations. 3- Test for conditions. 4- Sequence the execution of instructions. 5- Store data temporarily during execution in the defined R/W memory locations called the stack.

*To perform these operations the Mp requires:-

a) Registers. b) An arithmetic logic unit (ALU) & control logic. c) Internal buses (paths for information flow).

D 7

A 15 A 0

8085/

MPU

D 0 0

16 - bit memory address address bus

Data

memory decode

D) Stack pointer (sp):-

This 16-bit register used as memory pointer, it point to memory location in R/W memory called (the stack), the beginning of the stack is defined by loading 16-bit address in stack pointer (register).

*Flag – Register:-

The flag register contains 5-bit that are used as flags or indicator.

Any time 8085 executes an arithmetic or logic instruction.

S Z AC P CY

Where:-

S mean the sign bit and given:-

Logic 1 = (-ve).

Logic 0 = (+ve).

Z mean zero flag and given:-

Logic 1 = zero result.

Logic 0 = 1 result.

AC mean auxiliary carry and given:-

Logic 1 = there is a carry from bit 3 to bit 4.

Logic 0 = no carry.

P mean parity flag and given:-

Logic 1 = the number of ones in accumulator is even.

Logic 0 = the number of ones in accumulator is odd.

3- Peripheral or Externally Initiated Operations:-

External devices (or signals) can initiate the following operation for which individual pins on Mp chip are assigned: Reset, Interrupt, Ready, Hold.

A) Reset: when reset is activated all internal operations are suspended and the program counter is cleared.

B) Interrupt : the Mp can be interrupted from normal execution and asked to execute other instructions called "service routine" (emergency), Mp resumes its operation after that.

C) Ready : 8085 has pin called ready, if the signal is low Mp enters into wait state, this signal used to synchronized slower peripherals with Mp.

D) Hold : when hold pin activated by external signal Mp relinquishes control buses and allows the external peripheral to use the. For example:

Hold signal is used in direct memory access data transfer.