Program Execution and Timing

If the microprocessor is a powerful device in data-processing, it can also be the most dummiest device ever invented. A microprocessor cannot do anything without the program.

The microprocessor does only 2 things, Fetch data and Execute data.

The four (4) steps under fetch and execute are as follows;

1. Read data pointed by the program counter and store it to the instruction register .
2. Increment the program counter.
3. Decode/Execute the data at instruction register.
4. Goto 1.

Consider this program below;

Mem
0000 DB IN 12
0001 12
0002 D3 OUT 11
0003 11

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