CSE111: Great Ideas in Computer Science

CSE111: Great Ideas in Computer Science Dr. Carl Alphonce 219 Bell Hall Office hours: M-F 11:00-11:50 645-4739 alphonce@buffalo.edu

cell phones off (please)

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

One-bit Half Adder A B S C

One-bit Half Adder 0+ 0 0 (carry 0) A= 0 B = 0 S = ? C = ?

One-bit Half Adder 0+ 0 0 (carry 0) A= 0 0 0 0 B = 0 0 S = 0 1 0 0 1 0 C = 0

One-bit Full Adder A B S Cin Cout

Encoding machine instructions • Op-code + operands • Hardware decodes and executes

Computer Organization • Central Processing Unit (CPU) • Registers • General purpose (e.g. R1 – R16) • Special purpose (e.g. Program Counter and Instruction Register) • Arithmetic Logic Unit (ALU) • Memory

CSE111: Great Ideas in Computer Science