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Main Assembly Programming Input/Output Memory Computer Architecture Advanced Topics

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Question 4

This question assumes the machine architecture at the right. Note the stack pointer register, SP, is not part of the register file. SEL is a multiplexor used to select one of the inputs to the ALU.
Assume memory addresses require only one memory cycle to fetch or store (unlike the 68000). Bus Architechture

Show the machine code control sequence of the RTE (return from exception/interrupt) instruction as in the 68000 showing the register transfers at each step that implements the instruction. Include the instruction fetch sequence.

Answer

  1. WMFC, PCout, MARin, Read, Yin
  2. Sel2, Add, Zin
  3. Zout, PCin, [Yin]
  4. WMFC, MDRout, IRin
  5. SPout, MARin, Read,Yin
  6. Add, Zin, Sel 2
  7. WMFC, MDRout, STATUSin
  8. Zout, MARin, Yin, Read
  9. Add, Zin, Sel2
  10. Zout, SPin
  11. WMFC, MDRout, PCin, END



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