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This introductory course, led by Dr. Carl Alphonce at the University at Buffalo, covers fundamental concepts of computer science. Students will learn about the basic components of computers, including voltage manipulation, circuits, and logical gates. The course also emphasizes the difference between physical and logical perspectives of computing. Practical applications like flip-flops for memory will be explored, along with truth tables for AND, OR, and NOT operations. Students will engage in interactive sessions and have opportunities for hands-on practice to solidify understanding.
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CSE115: Introduction to Computer Science I Dr. Carl Alphonce 219 Bell Hall alphonce@cse.buffalo.edu
Announcements • If this is your first class: • print a syllabus from the course website • hand in signature form next class • Recitations start this week • Cell phones off
Today’s lessons • A computer is a very simple machine. • A computer manipulates voltages • Gates are used to control voltage flow • Circuits are combinations of gates • A flip-flop is a circuit that remembers • But first…
Name sign competition • Put your signs out! • 9:00 AM – Jeff • 1:00 PM – Nina • 3:00 PM – Alicia
physical vs. logical perspectives • Physical reality: • Logical view: Carries a HIGH voltage or a LOW voltage WIRE Carries a 1 or a 0 WIRE
AND gate output is on right 0 or 1 inputs are on left For which input values is output 1? For which input values is output 0?
OR gate output is on right inputs are on left For which input values is output 1? For which input values is output 0?
NOT gate input is on left output is on right For which input value is output 1? For which input value is output 0?
Flip-flop (a bit of memory!) R (reset) remembered value S (set)
Setting the flip-flopThe normal value of R and S is zero. R (reset) = 0 remembered value S (set) = 0
Setting the flip-flopTo store 1 in the flip-flop, we “raise” S to 1… R (reset) = 0 remembered value S (set) = 1
Setting the flip-flop…which makes the output of the OR gate 1. R (reset) = 0 remembered value 1 S (set) = 1
Setting the flip-flopThe NOT gate inverts this 1 value to 0, which becomes the second input to the upper OR gate. R (reset) = 0 remembered value 0 1 0 S (set) = 1
Setting the flip-flopSince both inputs of the upper OR gate are zero, its output is zero. R (reset) = 0 0 remembered value 0 1 0 S (set) = 1
Setting the flip-flopThe NOT gate inverts this 0 to a 1; this value becomes the second input to the bottom OR. R (reset) = 0 1 0 remembered value 0 1 1 0 S (set) = 1
Setting the flip-flopBecause the output of the bottom OR gate will now stay at 1, we can lower S to zero, and the circuit will stay in a stable state, with 1 as the remembered value! R (reset) = 0 1 0 remembered value 0 Resetting the flip-flopResetting the remembered value to zero is similar, except we raise, then lower, the value on R. 1 1 0 S (set) = 0