3. What are Instructions ?
The commands that microprocessor understand are called instructions
INSTRUCTION SETS: The complete ‘vocabulary’ of each chip is called Instruction Set
We will study the entire Z80 instruction set, we will study only those instructions which are
common to 8080 and 8085.
Also, we will not study the entire 8086/8088 instruction set but will omit the loop string instructions
since they have no counterpart in the 8-bit microprocessors
4. CPU Control Instructions
The NO Operation: The NO Operation instruction does exactly that: It does nothing. This is the
waste of time, and wasting time is what this instruction does best
USES:
The microprocessor is too fast; the NO operation is used to waste some amount of time
Filing of space in the program. When writing programs, we must sometimes insert additional
instructions into the middle of a program to alter the way it works or to fix a problem
The Halt Instruction: Called Halt, wait or break (depending on microprocessor). This instruction
has the obvious purpose of stopping the microprocessor. There is no go instruction. We will see
how that is done shortly, but there must be a way to stop the program. In some microprocessor
families this is not the only function of this instruction, but this is all we need to be concerned
with at this time
5. Data Transfer Instruction
Where Data is Transferred
Data is moved between registers or between registers and memory. The number of possible
combinations depends on the microprocessor and how many registers it has.
How Data is Transferred
‘Move’, ‘Load’, ‘Store’ and ‘Transfer’ are all common terms
When ‘Move’, ‘Load’, ‘Store’ and ‘Transfer’ is executed, a duplicate
of the data is actually being placed in the target register or destination
