A couple of people have reported this issue: the stack counter resetting to zero for no apparent reason.
Here's what's happening. It's called a race condition — when a circuit works or doesn't work depends too much on the timing of the gates. In this case, depending on what order Logisim evaluates certain gates, the signal sent to sc1 and sc0 can be temporarily 00. If, just out of bad luck, Logisim decides to look at the stack counter at this point, it will reset the stack counter to 0, even if later on sc1 and sc0 evaluate to something other than 00.
(BTW, this seems to be happening to people who for some reason decided to make sc1 and sc0 sub-circuits.)
You can check if this is what is happening to you by disconnecting the zero line to the stack counter:
If your counter doesn't reset by itself after this, then you might have this problem. (You can have other problems too.)
You can make the stack counter more forgiving, by having it reset only if the clock is low:
This more robust version was uploaded to this webpage.
The displays for the ALU controls (ALU d1 and ALU d0) were also flipped. The should look like this:
The fixed version is uploaded, but for most people, it would be easier to just swap the connections yourself.
Another bug in Homework 5, this time in the write up.
In the project description, it says that if the ALU controls have d1=1 and d0=1, then the ALU increments Port B. This is not correct. The ALU increments Port A. (This is the same behavior as the ALU from Homework 3).
The web site has been updated.
In Homework 5, there was a small bug in the wiring of the display for the stack control lines. The displays for sc1 and sc0 should be wired like this:
The circuits on this web site have been updated.
Homework 5 posted.
Homework 4 posted.
Prof. Chang's office hours on Thursday, April 25rd will be moved to Friday, April 26, 11am – 12pm.
Homework 3 posted.
Fixed main8c.c for Project 8. Testing of the bst_remove() function was buggy.
Updated bst.c for Project 8. Comments for bst_remove() were backwards between left and right.
Project 8 posted.
Project 7 posted.
Project 6 posted.
Professor Chang's office hours on Thursday, March 28 has been moved from 11:30am – 12:30pm to 12:00pm – 12:50pm.
Project 5 posted.
Our TA, Roshan Ghumare, will hold additional office hours on Wednesdays 10am – 12pm, starting Wednesday March 13.
Reminder: the Midterm Exam is on Thursday, March 14. See Tuesdays slides for topics: Slides12.pdf.
Project 4 posted.
The main3.c program for Project 3 is also available for copying directly on the GL file system at:
Homework 1 and 2 grades have been posted on Blackboard.
Project 3 posted.
Project 2 posted. The Project 2 Codeword Format is on a separate page.
Project 1 posted.
TA office hours are now listed on the contacts page.
You can also copy hello.asm and toupper.asm on the GL filesystem using:
cp /afs/umbc.edu/users/c/h/chang/pub/cs313/hello.asm .and
cp /afs/umbc.edu/users/c/h/chang/pub/cs313/toupper.asm .Don't forget the . at the end. It specifies the current directory as the target of the copy command.
Homework 2 posted: hw2.pdf (due Tuesday, February 12).
Lecture topics and slides are linked off the syllabus page. For example, here's today's lecture topics with links to the slides shown in class.
Homework 1 posted: hw1.pdf (due Tuesday, February 5).
First day handouts (PDF): course description, academic integrity policy, and syllabus. Hard copies will be distributed in class.
Web page up.
to Spring 2013 CMSC 313 Homepage