(a) IR ← M[PC] PC cannot provide address to memory. Address must be terransfred to AR first AR← PC IR ← M[AR]
(b) AC ← AC + TR Add operation must be done with DR. Transfer TR to DR first. DR ← TR AC ← AC + DR
I opcode Register Address
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(c) DR ← DR + AC Result of addition is transferred to AC (not DR). To save value of AC its content must be stored temporary in DR (or TR).
AC ← DR, DR ← AC (See answer to Problem 5.4(d)) AC ← AC + DR AC ← DR, DR ← AC