LC-3 Basics
| Type | Quiz 2 Material |
|---|
Legendary LC3 video:
https://www.youtube.com/watch?v=6hhNNj67w1E&t=2685s
Questions and Answers
What is a bus?
A 16-bit wire that transfers data between many components
Why can we only have one value on the bus at a time (what would happen otherwise)? What component do we use to control which value is on the bus?
- Only one value at a time to prevent short circuit
- Transit buffer
- Helps in making sure there is only one value on the bus
- Allow us to choose whether or not to write a value
What does the value in the PC represent?
- holds the current program counter-address of the next instruction to execute
- three ways to update PC
- PC + offset
- PC + 1
- Given a value for the PC via the bus
What does the value in the IR represent?
- holds the value of the current instruction
- having the correct value in the IR helps the FSM determine the current state and send the correct control signals
- a new value can be read from the bus (with signal LD.IR) and the current value is directly connected to relevant components
What is the role of the microcontroller in the LC-3
- Finite State Machine (FSM)
- Every instruction has a series of states to execute it
- Like in HW3, each state has
- A set of outputs (control signals like ALUK, LdReg, etc.)
- The next state to go to
- Ensure that correct operations take place while preventing short circuits
