**INSTRUCTION CYCLE**

Instruction cycle is defined as the time required to complete one instruction.The instruction cycle

consists of 1-6 machine cycle.

**MACHINE CYCLE**

Machine cycle is defined as the time required to complete one operation of accessing memory, I/O operation or

acknowlegding an external request. This cycle may consist of 3-6 T states.

**T-STATE**

T-state is defined as one subdivision of operation performed in one clock period. These internal subdivision are

in synchronisation with the system clock. And each T-state is precisely equal to one clock period.

**SIGN FLAG**

The flag is used to differentiate between signed and unsigned numbers. In a geven byte if D7 is 1, the number will be viewed as a negative number; if it is zero it will be viewed as a positive number.

**ZERO FLAG**

The zero flag is set when ALU operation leads to 0, and flag is reset if result is not zero.

**AUXILLARY CARRY**

In an arithmetic operation, when a carry is generated by digit D3 and passed to digit D4, AC flag is set. The flag is used internally for BCD operation and not available to programmer.

**PARITY FLAG**

After an arithmetic or logical operation if number of 1's in Accumulator is even it is set and if its odd it is reset.

**CARRY FLAG**

If an aritmetic operation results in a carry the flag is set otherwise it is reset. This also serve as a borrow flag for subtraction.

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