11/10/2006

A student writes:


Hi, Dr. Patt

In problem set #5, question 6, I don't understand what I am 
supposed to do. Maybe I am too stupid. Would you please 
to explain what is the meaning of "sets a bit" and "clears 
the specified bit"? And what is
"The index of the bit to set is specified in R1"? Thanks

Best Regards,
<<name withheld to protect the student who is jargon-challenged>>

Thank you for the email message, and no, you are not stupid.
In fact, I very much appreciate the questions, because the
jargon of setting and clearing bits may not be common terms
in many students' vocabularies ...yet.  They will be.

I have used the terms in class within the context of explaining
R/S latches some time ago, but clearly not often enough to have 
them stick.  No matter, I am happy to say it again:

Setting a bit = Writing a 1 into the location of a bit
Clearing a bit = Writing a 0 into the location of a bit

The word "index" is a common term to specify which of a sequence 
of items we are referring to.  So, in the context of problem 6 on
the problem set, the index is the bit number of the register.  The
most significant bit (MSB) has an index of 15, and the LSB as an index
of 0.

OK?

Good luck getting ready for the exam next Wednesday.

Yale Patt