Introduction to 8085 Microprocessor, Study notes of Electrical Engineering

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FACULTY OF ENGINEERING

Prepared by Prashant Kumar (Faculty ECE Department, FoE TMU)

POWERPOINT

PRESENTATION

On

8085 microprocessor

Content

• Introduction
• (^) Features
• Pin Configuration
• Architecture 0f 8085
• The 8085 Bus Structure
• Instruction Set
• Addressing Modes

Features

• 8 bit microprocessor(8085 microprocessor can read or write or perform arithmetic and logical operations on 8-bit data at time)
• It has 8 data lines and 16 address lines hence capacity is 216 = 64 kB of memory
• Cock frequency is 3 MHz
• It requires +5V power supply.
• It is a single chip NMOS device implemented with 6200 transistors.
• It provides 74 instructions with five addressing modes.
• It provides 5 hardware interrupt and 8 software interrupts.

Pin Configuration

• 40 pins classified into 6 groups:

1. Data bus
2. Address bus
3. Control & status lines
4. Externally generated
5. Serial interface
6. Power supply & clock

Pin Configuration cont…

1. Address Bus (A15-A8 and AD7-AD0): The microprocessor 8085 has 16 bit address lines from A15-A8 and AD7-AD0. These lines are used to transfer 16 bit address of memory as well as 8-bit address of I/O ports.
2. Data Bus: The lower 8 lines (AD7-AD0) are often called as multiplexed data lines.

CONTROL LINES

• RD : Read: This is active low signal which indicates that the selected I/O or memory device is to be read and also is available on the data bus.
• WR : Write: This is active low signal which indicates that the data on data bus are to be written into a selected memory location.
• IO/ M : (Input / Output / Memory): This is used to select either Input / Output devices or memory operation. When it is high it indicates an I/O operation and when it is low, it indicates a memory operation. STATUS LINES
• Status Pins (S1, S0): The microprocessor 8085 has two status pins as S1, S0 which is used to indicate the status of microprocessor or operation which is performed by microprocessor.

Architecture 0f 8085

1. ALU
2. Timing and Control Unit
3. General Purpose Registers
4. Program Status word
5. Program Counter
6. Stack Pointer
7. Instruction Register and Decoder 8. Interrupt Control 9.Serial I/O Control 10.Address Bus
8. Data Bus

REGISTERS The Registers are of 8-bit & 16-bit size used for different purposes A- Accumulator – This is an special purpose register. All the ALU operations are performed with reference to the contents of Accumulator. B,C,D,E,H,L – General purpose registers. These registers can also used for 16-bit operations in pairs. The default pairs are BC, DE & HL.

F – Flag register – This register indicates the status of the ALU operation. PC – Program Counter – This is a 16-bit register used to address the memory location from where an instruction is going to be executed.

ALU – Arithmetic & Logic Unit ALU of 8085 performs 8-bit arithmetic & logical operations. The operations are generally performed with Accumulator as one of the operands. The result is saved in accumulator register. Timing & Control Unit This unit works as the brain of the CPU and generates all the timing and control signals to perform all the internal & external operations of the CPU. Instruction Decoder & Machine Cycle Encoder Unit This unit decodes the op-code stored in the Instruction Register (IR) and encodes it for the timing & control unit to perform the execution of the instruction.

The 8085 Bus Structure The 8-bit 8085 CPU (or MPU – Micro Processing Unit) communicates with the other units using a 16-bit address bus, an 8-bit data bus and a control bus.

Addressing Modes

• Immediate (MOV A,B ;ADD B; SUB E;ANA C)
• Register (MVI A,05H;LXI B, 20AEH; ADI 05H;ORI 07H)
• Direct (LDA 4500H;STA 7500H;IN 09H;OUT 70H)
• Indirect (MOV A, M;MOV M,A;ADD M;ORA M)
• Implied(implicit) (HLT; NOP;RST;RET)

Thanks