Chapter 3 Continued Logic Gates Logic Chips Combinational Logic Sequential Logic Flip Flops Registers Memory Timing State Machines.
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Chapter 3 Continued Logic Gates Logic Chips Combinational Logic Sequential Logic Flip Flops Registers Memory Timing State Machines
Lab Breadboard Strips 4 Sets of connected pin holes run horizontally on the top and bottom of the strip (good for running/connecting power and ground) Approximately 60 sets of connected pin holes run vertically in the middle of the strip (good for connecting power to pins and connections between pins) Note: Use Bell wire to make connections. You might want to color code wires by function.
Logical Completeness Can implement ANY truth table with AND, OR, NOT. 1. AND combinations that yield a "1" in the truth table. 2. OR the results of the AND gates. ALSO: Can implement ANY truth table with ONLY NANDS. Can implement ANY truth table with ONLY NORS.
JK Flip Flop J K | Qn+1 0 0 | Q n 0 1 | 0 1 0 | 1 1 1 | not Q n
JK as a Universal Flip Flop JK as an SR – use set and pre inputs JK as a Toggle – connect J and K JK as a D – connect NOT J to K
Register A register stores a multi-bit (vector) value. –We use a collection of D-latches, all controlled by a common write enable pulse, call it WE. –When the write enable WE=1, the n-bit value D is written to register.
2 2 x 3 Memory address decoder word selectword WE address write enable input bits output bits
More Memory Details Two basic kinds of RAM (Random Access Memory) Static RAM (SRAM) –fast, maintains data as long as power applied Dynamic RAM (DRAM) –slower but denser, bit storage decays – must be periodically refreshed. Refreshing interferes with regularity of execution of instruction stream. Also, non-volatile memories: ROM, PROM, flash, …
Alternative Logic “Family” Choices Totempole: High or Low output level (Most Common) Line always at a 1 level or 0 level Tristate: High, Low, or Open (Good for BUS application) Like Totempole, but has third state – open state Open Collector, Open Drain, Wired-OR: (Older alternative to Tristate – still used, but more susceptible to noise) Line is nominally at a 1 level or 0 level – line is “pulled” to non-nominal level. Outputs of and gates can be connected directed together to create an “OR condition. Differential: (Used for driving signals a distance. Good noise immunity) Uses a pair of lines – the “level” is the difference of signals on the two lines.
Combinational vs. Sequential Circuits Combinational Circuit –always gives the same output for a given set of inputs example: adder always generates sum and carry, regardless of previous inputs Sequential Circuit –has memory - “stores” information, –output depends on stored information (state) plus input so a given input might produce different outputs, depending on the stored information –example: ticket counter advances when you push the button output depends on previous state –useful for building “memory” elements and “state machines”