Chapter 03 - Digital Logic

# Logical completeness byu csecen 124 chapter 3 digital

• Notes
• 62

This preview shows page 32 - 42 out of 62 pages.

Logical Completeness

Subscribe to view the full document.

BYU CS/ECEn 124 Chapter 3 - Digital Logic 33 Storage Elements Everything so far has been combinational logic the output is strictly a function of the current inputs Computing systems need storage elements for holding previously computed values for saving state Two types of locks: Sequential Logic 4 1 8 4 Combinational – Success depends only on the values , not the order in which they are set. 30 15 5 10 20 25 Sequential - Success depends on the sequence of values (e.g, R-13, L-22, R-3).
BYU CS/ECEn 124 Chapter 3 - Digital Logic 34 Bi-Stability = Key to Memory When there are 2 stable states - a bi-stable circuit RS Latch Sequential Logic 0 1 1 This is also a stable state – it will sit like this forever 1 0 0 This is a stable state – it will sit like this forever q q s r q q s r 1 1 0 1 1 1 1 0

Subscribe to view the full document.

BYU CS/ECEn 124 Chapter 3 - Digital Logic 35 RS Latch – Bi-Stable Circuit Sequential Logic 0 1 1 0 1 0 0 1 1 1 0 1 q q s r 1 1 1 0 This is also a stable state – it will sit like this forever q q s r This is a stable state – it will sit like this forever 1 0 1 1 1 1 0 1 1 1 1 0
BYU CS/ECEn 124 Chapter 3 - Digital Logic 36 Gated D Latch Output q gets value from input d only when we is high we stands for write enable , think of it as a load signal s r q q d we LATCH Symbol WE D Q D-Latch Symbols are abstractions! Latch

Subscribe to view the full document.

BYU CS/ECEn 124 Chapter 3 - Digital Logic 37 Register A computer register is a place to store a collection of bits Very fast memory Numbered right to left (LSB on the right) D-Latch d0 q0 D-Latch d1 q1 D-Latch d2 q2 D-Latch d3 q3 we REGISTER Symbol Register d q we Latch
BYU CS/ECEn 124 Chapter 3 - Digital Logic 38 Memory A collection of addressable locations Address selects which location to read from or write to Memory address q n we d m m A memory with n address wires has 2 n locations. The number of data wires in equal the number of data wires out. Memory is changed with we is asserted. q always reflects the contents stored at the addressed memory location. Memory can be viewed as a large collection of slower registers. Memory

Subscribe to view the full document.

BYU CS/ECEn 124 Chapter 3 - Digital Logic 39 Building a Memory From Latches 2-to-4 Decoder a1 a0 00 01 10 11 Register Register Register Register we we we we writeEnable d input q output This is a functional view. The key parts are: address decoder memory cells (registers) output selector (mux) Memory address q n we d m m MEMORY Symbol n = 2 address q 0 q 1 q 2 q 3 Memory
BYU CS/ECEn 124 Chapter 3 - Digital Logic 40 A 12-Bit Memory 4 words, each 3 bits wide Word line “00” Word line “01” Word line “10” Word line “11” Latch Only one word line is high at any given time. Memory

Subscribe to view the full document.

BYU CS/ECEn 124 Chapter 3 - Digital Logic 41 Reading a 12-Bit Memory Each column forms a sort of multiplexor Only one of the AND gates in the column will be enabled. Thus, they allow one row out of 4 to be selected for reading.
You've reached the end of this preview.
• Fall '08
• Staff
• Logic gate, Finite State Machine, BYU CS/ECEn

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern