Sun, 8th Nov 2015, 16:43 Re: Question on #19 on Problem Set 5

A student writes:


> Hello Dr. Patt,
> For question #19, I notice that there are some signals that are set to
> IR[8:6] and one that is set to BaseR. As all of the instructions for the
> LC-3 ISA that use a Base Register place it in bits 8:6, are we to assume
> that IR[8:6] and BaseR are the same thing? If not, how can I figure out
> what input BaseR is?
>
> Thanks,
> Dr. Patt's #1 Fan


Another student decides to deny me the opportunity to come up with a signature
for him.  ...and this student adds flattery on top of it!

Now to answer his question: No, you can not assume that.  In state A, it says
ADDR1MUX = BaseR.  ADDR1MUX is taking its source from one of two places.  What
are they?  BaseR specifies which of the two sources.

As to IR[8:6], why is this incorrect?  Which register from the register file
will be the source that ADDR1MUX uses?  How do you know?  Hint: Look carefully
at the data path and all the control signals in State A.

Good luck finishing the problem set by class time tomorrow.



Yale Patt