Suppose that the following instructions are found at the given locations in memo

Question

Suppose that the following instructions are found at the given locations in memory:

   Location     Contents

    00    lda 20
    01                 add 21
    02                 sto 21
    03       hlt            
    20                 dat 005        
    21                 dat 008

Show the contents of registers PC, MAR, MDR, and Acc (accumulator) at the conclusion of the instruction at location 01, i.e. before the instruction at 02 is fetched. (Hint: This question is constructed so that it doesn’t make any difference whether the addresses are decimal or hexadecimal numbers. The dat constants are decimal.)

Explain how the Little Man Computer can use the same operation code (9) for both input and output.

Explanation / Answer

PC (program counter ) is can also be called as instruction pointer holds the address of next instruction.

Here at location 01 it holds address of next instruction I.e., 02

MAR Memory address Register is a CPU register holds the address of data to be fetched from memory and data addressed by MAR is fed into MDR Memory data register.

Here MAR holds Address of 21 and MDR holds 21.

The add 21 adds the content of 21 and accumulator which is already loaded with 5

Now the accumulator holds 13

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