Dr. Patt,
     On question 8 of homework set 3, do you want
     us to write in the chart what the registers
     do/load (words) or do you want the actual codes
     (numbers) being loaded into them from the examples?
     << name withheld to protect ... >> 

So, the statement of the problem says:

     In each location of the table below, enter the opcodes which write
     to the corresponding register (row) during the corresponding phase
     (column) of the instruction cycle.

I am curious as to where the problem is, and hopefully the student will write me again telling me what is ambiguous about this. Perhaps I have just been too close to this too long. Anyway:

Each location in the table: we have so many rows, so many columns. Each location is specified by a row (register) and column (instruction phase). For example, row 2, column 4 is row IR, column Fetch data. You would write ADD in this location if the ADD instruction writes into the IR during the Fetch Data phase fo the instruction cycle.

I have given you three different opcodes: ADD, LDR, and JMP. Your job is write ADD in every location where the register (row) is written into during the corresponding phase (col) of the instruction cycle. Repeat for LDR, JMP.

Said a totally different way:

Take the ADD instruction. As you go from Fetch instruction to Store Result, in what phases (if any) are the various registers written into. For every case where a register is written in a phase, write ADD in that corresponding location. Now repeat for LDR and JMP.

When you are done, the table will have many ADD, LDR and JMP written into it. Some locations may have nothing written into it. Some locations may have one or more written into it.


Yale Patt