8085 Microprocessor

8085 Microprocessor

8085 Microprocessor is an 8-bit processor suitable for a wide range of application.8085 Microprocessor is a single-chip, NMOS device implemented with approximately 6200 transistors on a 164 * 222 mil chip contained in a 40-pin dual-in-line package.

8085 Microprocessor

8085 Microprocessor Architecture

Most Important Point Of 8085 Microprocessor :

1.  Intel 8085 is an 8-bit microprocessor it can accept, process, or provide 8-bit data simultaneously.
2. It operates on a single +5V power supply and operates on clock cycle with 50 % duty cycle.
3. It has 16 address lines, here it can access 64 kbytes of memory.
4. It provides 8-bit I/O addresses to access 256 I/O ports.
5. It can operate with a 3 MHz clock Frequency.
6. It has serial I/O control which allows serial communication.
7. It has a mechanism by which it is possible to increase its interrupt handling capacity.
8. The 8085 has an ability to share system bus with direct memory access controller. This feature allows to transfer large amount of data from I/O device to memory or from memory to I/O device with high speeds.

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8085 consists of various functional units :

1. Registers

8085 Microprocessor | It includes six 8-bit registers (B, C, D, E, H, and L), one accumulator, one flag register and two 16-bit registers(SP and PC). All these registers are accessible to programmer and hence they are included in the programmer's model.

The 8085 Registers are classified as General Purpose Registers, Temporary Registers, Special Purpose Registers, Sixteen Bit Registers.

2. Arithmetic Logic Unit (ALU)

8085 Microprocessor | ALU performs arithmetic and logical functions on eight bit variables.The arithmetic unit performs bitwise fundamental arithmetic operations such as addition and subtraction. The logic unit performs logical operations such as  AND, OR and EX-OR.

3. Instruction Decoder

8085 Microprocessor | The processor first fetches the opcode of instruction from memory and stores this opcode in the instruction register. It is then sent to the instruction decoder. The instruction decoder decodes it and accordingly gives the timing and control signals which control the register, the data buffers ALU and external peripheral signals depending on the nature of the instruction.

4. Address Buffer

This is an 8-bit unidirectional buffer.it is used to drive external high order address bus (A15-A8). It is also used to tri-state the high order address bus under certain conditions such as reset, hold, halt, and when address lines are not in use.

5. Incrementer/Decrementer Address Latch

This 16-bit register is used to increment or decrement the contents of program counter or stack pointer as a part of execution of instructions related to them.

6. Interrupt Control

The processor fetches, decodes and executes instructions in a sequence. sometimes it is necessary to have processor the automatically execute one of a collection of special routines whenever special condition exists within a program or the microcomputer system. The occurrence of this special condition is referred as interrupt.

7. Serial I/O Control

The 8085's serial I/O Control provides two lines, SOD and SID for serial communication. the serial output data (SOD) line is used to send data serially and serial input data (SID) line is used to receive data serially.

8. Timing And Control Circuitry

The control circuitry in the processor 8085 is responsible for all the operations. the control circuitry and hence the operations in 8085 are synchronized with the help of clock signal. 

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