Questions

  1. Write the Register Transfer Description for the instruction LDI.

  2. Write the Effective Address (EA) for the instructions that use Direct/Pc-Relative addressing.

  3. Does the instruction LEA calculate an Effective Address? Why is LEA different from the other Load instructions?

  4. How many memory accesses (read or write) are made during the entire instruction cycle for an STI instruction?

  5. Which bits can represent the SR1 from the instruction register?

  6. When are condition codes in the LC-3 written to?

  7. Which instruction use a bit flag to implement two different addressing modes for the same instruction?

  8. In the LC3 data path, the output of the address adder goes to both the MARMUX and the PCMUX, potentially causing two very different register transfers to take place. Why does this not happen?

  9. Imagine we want to save an extra Opcode in the LC-3 by combining two of the instructions, and using a bit flag to implement two different addressing modes. Which instructions could you combine? Write out the layout of the new combined instruction, and specify how it implements both previous instructions.