1. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني The 8085 Microprocessor Architecture

2. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 8085 INTRODUCTION The features of INTEL 8085 are : It is an 8 bit processor. It is a single chip device with 40 pins. It has multiplexed address and data bus.(AD 0 -AD 7 ). It works on 5 Volt dc power supply. The maximum clock frequency is 3 MHz while minimum frequency is 500kHz. It provides 74 instructions with 5 different addressing modes.

3. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 8085 INTRODUCTION It provides 16 address lines so it can access 2^16 =64K bytes of memory. It generates 8 bit I/O address so it can access 2^8=256 input ports. It provides 5 hardware interrupts : TRAP, RST 5.5, RST 6.5, RST 7.5,INTR. It provides Acc,one flag register,6 general purpose registers and two special purpose registers(SP,PC). It provides serial lines SID,SOD. So serial peripherals can be interfaced with 8085 directly.

4. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 4 The 8085 Architecture The 8085 uses three separate busses to perform its operations The address bus. The data bus. The control bus.

5. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 5 The Address Bus 16 bits wide (A 0 A 1 …A 15 ) Therefore, the 8085 can access locations with numbers from 0 to 65,536. Or, the 8085 can access a total of 64K addresses. “Unidirectional”. Information flows out of the microprocessor and into the memory or peripherals. When the 8085 wants to access a peripheral or a memory location, it places the 16-bit address on the address bus and then sends the appropriate control signals.

6. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 6 The Data Bus 8 bits wide (D 0 D 1 …D 7 ) “Bi-directional”. Information flows both ways between the microprocessor and memory or I/O. The 8085 uses the data bus to transfer the binary information..Since the data bus has 8-bits only, then the 8085 can manipulate data 8 bits at-a-time only. The Control Bus the control bus is made up of a number of single bit control signals.

7. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 7 Operation Types in a Microprocessor All of the operations of the microprocessor can be classified into one of three types: -Microprocessor-Initiated Operations -Internal Operations -Peripheral-Initiated Operations

8. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 8 Microprocessor-Initiated Operations These are operations that the microprocessor itself starts. These are usually one of 4 operations: Memory Read Memory Write I/O Read (Get data from an input device) I/O write (Send data to an output device)

9. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 9 Internal Data Operations The 8085 can perform a number of internal operations. Such as: storing data, Arithmetic & Logic operations, Testing for condition, etc. To perform these operations, the microprocessor needs an internal architecture similar to the following: AccumulatorFlags BC DE HL Program Counter Stack Pointer DataAddress816

10. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 10 The Internal Architecture Registers Six general purpose registers used to store 8-bit data during a program execution The registers are identified as B, C, D, E, H, and L They can be combined as register pairs: BC, DE, and HL to perform 16- bit operations Accumulator 8-bit register that is part of the ALU Used to store 8-bit data and in performing 8-bit arithmetic and logical operations, and in storing the results op operations

11. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 11 The Internal Architecture Flag: It is a group of 5 flip flops used to know status of various operations done. The Flag Register along with Accumulator is called PSW or Program Status Word. The Program Counter (PC) This is a register that is used to control the sequencing of the execution of instructions. This register always holds the address of the next instruction. Since it holds an address, it must be 16 bits wide.

12. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 12 The Internal Architecture The Stack pointer The stack pointer is also a 16-bit register that is used to point into memory. The memory this register points to is a special area called the stack. The stack is an area of memory used to hold data that will be retreived soon. The stack is usually accessed in a Last In First Out (LIFO) fashion.

13. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني Flag Register Flag Register is given by: S:Sign flag is set when result of an operation is negative. Z:Zero flag is set when result of an operation is 0. Ac : Auxiliary carry flag is set when there is a carry out of lower nibble or lower four bits of the operation. CY : Carry flag is set when there is carry generated by an operation. P: Parity flag is set when result contains even number of 1’s. Rest are don’t care flip flops. S Z X AC AC X P X CY CY

14. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 14 Externally-Initiated Operations External devices can initiate (start) one of the 4 following operations: Reset All operations are stopped and the program counter is reset to 0000. Interrupt The microprocessor’s operations are interrupted and the microprocessor executes what is called a “service routine”. This routine “handles” the interrupt, (perform the necessary operations). Then the microprocessor returns to its previous operations and continues.

15. نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 15 Externally-Initiated Operations Ready The 8085 has a pin called RDY. This pin is used by external devices to stop the 8085 until they catch up. As long as the RDY pin is low, the 8085 will be in a wait state. Hold The 8085 has a pin called HOLD. This pin is used by external devices to gain control of the busses. When the HOLD signal is activated by an external device, the 8085 stops executing instructions and stops using the busses. This would allow external devices to control the information on the busses. Example DMA.