This video completely explains how microprocessor 8085 works. Its shows full architecture along with all bus controls. With good animation work the flow of data and address from one place to another place are explained in detail manner.
Acumulator:-It is a 8-bit register which is
used to perform airthmetical and logical operation. It stores the output of any
operation. It also works as registers for i/o accesses.
Temporary
Register:-It is a
8-bit register which is used to hold the data on which the acumulator is
computing operation. It is also called as operand register because it provides
operands to ALU.
Registers:-These are general purposes
registers.Microprocessor consists 6 general purpose registers of
8-bit each named as B,C,D,E,H and L. Generally theses registers are
not used for storing the data permanently. It carries the 8-bits
data. These are used only during the execution of the instructions.
These registers
can also be used to carry the 16 bits data by making the pair of 2 registers.
The valid register pairs available are BC,DE HL. We can not use other pairs
except BC,DEand HL. These registers are programmed by user.
ALU:-ALU performs the airthmetic
operations and logical operation.
Flag
Registers:-It
consists of 5 flip flop which changes its status according to the result stored
in an accumulator. It is also known as status registers. It is connected to the
ALU.
There are
five flip-flops in the flag register are as follows:
1.Sign(S)
2.zero(z)
3.Auxiliary
carry(AC)
4.Parity(P)
5.Carry(C)
The bit
position of the flip flop in flag register is:
All of
the three flip flop set and reset according to the stored result in the
accumulator.
1.Sign- If D7 of the result is 1 then
sign flag is set otherwise reset. As we know that a number on the D7 always
desides the sign of the number.
if D7 is
1: the number is negative.
if D7 is
0: the number is positive.
2.Zeros(Z)-If the result stored in an accumulator
is zero then this flip flop is set otherwise it is reset.
3.Auxiliary
carry(AC)-If any
carry goes from D3 to D4 in the output then it is set otherwise it is
reset.
4.Parity(P)-If the no of 1's is even in the
output stored in the accumulator then it is set otherwise it is reset for the
odd.
5.Carry(C)-If the result stored in an
accumulator generates a carry in its final output then it is set otherwise it
is reset.
Instruction
registers(IR):-It is a
8-bit register. When an instruction is fetched from memory then it is stored in
this register.
Instruction
Decoder:-
Instruction decoder identifies the instructions. It takes the informations
from instruction register and decodes the instruction to be performed.
Program
Counter:-It is a
16 bit register used as memory pointer. It stores the memory address of the
next instruction to be executed. So we can say that this register is used to
sequencing the program. Generally the memory have 16 bit addresses so that it
has 16 bit memory.
The
program counter is set to 0000H.
Stack
Pointer:-It is
also a 16 bit register used as memory pointer. It points to the memory
location called stack. Generally stack is a reserved portion of memory where
information can be stores or taken back together.
Timing
and Control Unit:-It
provides timing and control signal to the microprocessor to perform the various
operation.It has three control signal. It controls all external and internal
circuits. It operates with reference to clock signal.It synchronizes all the
data transfers.
There are
three control signal:
1.ALE-Airthmetic Latch Enable,It
provides control signal to synchronize the components of microprocessor.
2.RD- This is active low used for
reading operation.
3.WR-This is active low used for
writing operation.
There are
three status signal used in microprocessor S0, S1 and IO/M. It changes its
status according the provided input to these pins.
Serial
Input Output Control-There are
two pins in this unit. This unit is used for serial data communication.
Interrupt Unit-There are 6 interrupt pins in this
unit. Generally an external hardware is connected to these pins. These pins
provide interrupt signal sent by external hardware to microprocessor
and microprocessor sends acknowledgement for receiving the interrupt
signal. Generally INTA is used for acknowledgement.