Links Comments Header & Footer Text Question #6 14 marks!: Consider the followin

Question

Links Comments Header & Footer Text Question #6 14 marks!: Consider the following machine instruction. EA is the effective address that resides in AR during time T4. Assume that the adder and logic circuit can perform the exclusive- OR operation AC AC DR. Give the minimunn sequence of register transfer statements needed to execute each of the listed instructions starting from timing T4. Note that the value in AC should not change unless the instruction specifies a change in its content. You can use TR to store the content of AC temporary or you can exchange DR and AC. Symbol Opcode XOR | 000 | XCH | 010 Symbolic designation Description in words | MEAI CACMIE/ | Exclusive-OR to memory |MIE/ CACAC ME/Exchange AC and memory!

Explanation / Answer

For 1st instruction XOR:

T4: DR <-- M[AR]

T5: AC <-- AC DR

T6: M[AR] <-- AC

Here 3 register transfer instructions will be needed. First, to transfer the contents of EA to DR. Second, to perform XOR of AC and DR and place the result into the Register AC. And finally moving back the result from AC to memory EA.

For second instruction XCH:

T4: DR <-- M[AR]

T5: M[AR] <-- AC, AC <-- DR, SC <-- 0

Here 2 register transfer instructions are required. First to transfer the value at EA to DR and second to copy the contents of AC to EA, and DR to AC.

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