Intel 8085 is a 8-bit
microprocessor. It was the most successful 8-bit microprocessor. Here is an
overview of this.
In 8085 there are mainly three
components:
1) Arithmetic and Logical Unit(ALU)
2) Control Unit(CU)
3) Registers
1. ALU performs the arithmetic and logical operations like Add,
Sub, Increment, Decrement, OR, AND, Complement etc. ALU uses the accumulator to
hold the first operand and after operation accumulator holds the result. Second
operand is stored within the temporary register.
Another registrer called Flag
register is associated with the ALU. Flag registershows the status of result
after arithmetic or logical operation.
Flag is a 8-bit register out of that
5 shows the status and the remainig five bits are undefined. The five flags are
as follows:
1. Carry flag: if after the
arithmetic operation a carry is generated, Carry flag becomes 1 otherwaise the
value is zero.
2. Parity flag: Parity bit is
used for error detection in data. 8085 uses even parity method for error
detection. If the number of ones in result are even parity flag becomes,
othewase one.
3. Auxillary carry flag: if a
carry is generated fron lower nibble(A3-A0) towards the higher nibble(A7-A4)
than Auxirry carry becomes one otherwase the value is zero.this flag is used in
case of BCD operations.
4. Zero flag: This flag tells
that wether contents of register are zero or non zero? If zero flag is set(1)
that means register contents are zero.
5. Sign flag: the value of this flag
is equal to the MSB of accumulator. In case signed arithmetic it shows the sign
of result i.e. possitve or negative. If sign flag is set than result is
negative otherwase the result is possitive.
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Diagram of Intel 8085 Microprocessor
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