Lab 5 Tips

Lab 5 deals with creating an LFSR and then a state machine. Before you created 
a state machine with us giving you the next state logic and the amount of FD 
flipflops needed. In this case, we will be giving you specs on what the state 
machine should do, but not exactly how to build it. That is up for you to decide 
on how it should be designed. This is a short exposure to what you will be 
experiencing when on the project.

KEY: Learn to build an entire system out of scratch with just a certain baseline 
of requirements.

Click here for a TXT version of the notes.

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Revisions to Lab 5:

- The lab handout posted on the website is very outdated and has yet to be 
changed. Follow the revisions below to make your lab easier. Besides, some of 
the stuff do not exist anymore.

- The counter stated in the lab handout: rather use the CC8RE counter. Ignore 
the CEO line.

- When they say attach the Lab5.sch file, the file does not exist anymore. 
Instead, attach the lab5lib like you have with all the other labs and use the IO 
macro block that we have provided. The connections are all ready for you.

- Again you can find these librarys in \\fileservice\cs150 and they will be in 
the Lab5 folder. There are 2 folders, us the one that says Lab5 and nothing else.

- The lab handout also states that when you are done with MODE 1, then introduce 
an error into the ROM and do MODE 1 and MODE 0. However, we have provided a 
macro block called ROM_ERR that already has an error. Just replace the ROM block 
with ROM_ERR.

Tips and Comments:

- When designing your LFSR, you will need FD flipflops that can reset and that 
take in an enable signal that either disables or enables the flipflop to read 
the next new value on the next clock edge. I would suggest using an FDRE flip
flop.

- MODE: This is an important one. The way mode is changed by the SPARE button. 
However SPARE is a debounced signal which will only hold high for a clock cycle. 
MODE on the other hand is a signal that either stays high or stays low by using 
the SPARE button. So in fact, SPARE toggles the value of mode. 

- If you wire up MODE straight to the SPARE output on the IO block, MODE will 
only go high for a single clock cycle. It will never stay high. You need to fix 
this problem. Find a way to toggle the value of MODE and keep it's state after 
toggling. 

- If you are actually reading this, the solution is at the bottom of the tips.

- Also questions have been asked why there is a MODE input into the IO block. 
The reason for it is that the block provides an indicator, CR-3 (the dot LED), 
as an indicator of what mode you're in, or else it would be hard to determine. 
When the LED is on, then MODE=1, and when the LED is off then MODE=0.

- When designing your LFSR or your state machine, before downloading on the 
board it might be useful to simulate your logic block just to know that the 
logic is functioning correctly and state's are transitioning and outputs are 
going high or low when they should.