Thursday, October 01, 2009 11:40 PM,

A student writes:



	 I read in the problem set we are allowed to load bit masks in memory 
	 locations after the HALT instruction. So my question is can we also 
	 load other values in memory locations before our program executes?
	 
	 Thank You,
	 <<name withheld to protect the student who has some other constants to 
	 load>>



The short answer: Sure.  By now, you understand very well the instruction 
cycle.  So, you know that your program will get executed instruction by 
instruction according to the contents of the program counter until the program 
halts.  Execution will start with the instruction whose address is initially 
in the PC, which you have specified in the first file you create.  As long as 
there are no branch instructions, the instructions executed will proceed 
sequentially.  When a branch is encountered, the PC may be changed 
dramatically, and execution will continue from there.
Once the halt instruction is executed, that will be it.  No more instructions 
will be executed.

THEREFORE, anything in memory AFTER the halt instruction will never get 
fetched and never get executed.  Feel free to use those locations for whatever 
you wish - your girlfriends phone number if you wish, provided of course she 
has a 16 bit binary telephone number.

Good luck finishing the program.

Yale Patt