8085 was developed &
manufactured by Intel corp. It took the place of 8080.
- It is a 8 bit microprocessor.
- It has 3Mhz speed.
- The 8085 microprocessor family can address 64K
bytes of memory which is used for both code space and data space.
- 8085 can access up to 256 I/O devices.
- Memory is accessed by 20 pins.
- 8 address high
pins and 8 pins are used both for the 8 address low signals and for
the 8 data signals.4 pins are used for control purpose.
- 8085 requires only a +5V power supply.
This microprocessor has seven 8-bit registers named A, B, C, D, E, H, and L,
where A is the 8-bit accumulator and the other six can be used as independent
byte-registers or as three 16-bit register pairs, BC, DE, and HL.
Stack Pointer (Sp):-
1.The stack pointer is also a 16-bit register
used as a memory pointer.2.It points to a memory location in R/W memory,
called the stack.
3.The beginning of the stack is defined by
loading a 16-bit address in the stack pointer (register).
Program Counter (PC):-
1.This 16-bit register sequencing the execution
of instructions. 2.It is a memory pointer. Memory locations have
16-bit addresses, and that is why this is a 16-bit register.
3.The function of the program counter is to
point to the memory address of the next instruction to be executed.
4.When an opcode is being fetched, the program
counter is incremented by one to point to the next memory location.
Temporary Register: It is used to
hold the data during the arithmetic and logical operations.
Instruction Register: When
an instruction is fetched from the memory, it is loaded in the instruction
Instruction Decoder: It gets the
instruction from the instruction register and decodes the instruction. It
identifies the instruction to be performed.
Arithmetic and Logic Unit (ALU):
1.It is used to perform the arithmetic
operations like addition, subtraction, multiplication, division, increment
and decrement and logical operations like AND, OR and EX-OR.2.It receives the data from accumulator and
3.According to the result it set or reset the
I/O Control: It has two control signals named SID and SOD for serial data
Timing and Control unit:
1.It has three control signals ALE, RD (Active
low) and WR (Active low) and three status signals IO/M(Active low), S0 and
S1. 2.ALE is used for provide control signal to
synchronize the components of microprocessor and timing for instruction to
perform the operation.
3.RD (Active low) and WR (Active low) are used
to indicate whether the operation is reading the data from memory or
writing the data into memory respectively.
4.IO/M(Active low) is used to indicate whether
the operation is belongs to the memory or peripherals.
Interrupt Control Unit:
:-It receives hardware interrupt signals and
sends an acknowledgement for receiving the interrupt signal.