Fri, 6th Nov 2015, 17:53 Re: ee 306

A student writes:

> > Hello Dr. Patt. I am a student in your 306 class. I had a question about
> > the data path control signal of the lc3, specifically the SR1MUX. I cannot
> > find it in the data path. I am assuming that it is hidden that it is doing
> > something with the REG FILE, but I am not sure what it is doing exactly and
> > how it is implemented. Where is the SR1MUX and what does it do? Thank you!
> >
> > <<name withheld to protect the student who asks where the SR1MUX is hiding>>

You are right, the SR1MUX is not on page 570 with most of the data path.
It is on page 574 with some other structures that you will need.

Indeed, you are right, it is doing something with the register file,
as is DRMUX which you did not ask about.  SR1MUX identifies which register
to source to the ALU and DRMUS identifies which register to load the data
that is on the bus.

For example, if you are doing an ADD, you want IR[8:6] to identify the
register that is sourced to the ALU.  If you are doing ST, you want IR[11:9]
to identify the register that is sourced through the ALU and onto the bus.
SR1MUX allows you to obtain the appropriate register number from different

I am happy to see you are preparing for the second midterm.  Good luck!

Yale Patt