ee121 john wakerly lecture 6
Download
Skip this Video
Download Presentation
EE121 John Wakerly Lecture #6

Loading in 2 Seconds...

play fullscreen
1 / 34

EE121 John Wakerly Lecture #6 - PowerPoint PPT Presentation


  • 161 Views
  • Uploaded on

EE121 John Wakerly Lecture #6. Adders Multipliers Read-Only Memories Barrel-Shifter Design Example. 4-bit comparator. EQ_L. Equality Comparators. 1-bit comparator. 8-bit Magnitude Comparator. Other conditions. Comparators in ABEL. Equality checking PEQQ = ([P7..P0] == [Q7..Q0]);

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' EE121 John Wakerly Lecture #6' - gafna


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
ee121 john wakerly lecture 6

EE121 John Wakerly Lecture #6

Adders

Multipliers

Read-Only Memories

Barrel-Shifter Design Example

comparators in abel
Comparators in ABEL
  • Equality checking
    • PEQQ = ([P7..P0] == [Q7..Q0]);
    • PEQQ_L = !([P7..P0] == [Q7..Q0]);
    • 16 product terms
  • Magnitude comparison
    • PGTQ = ([P7..P0] > [Q7..Q0]);
    • PGTQ_L = !([P7..P0] > [Q7..Q0]);
    • 255 product terms (try it in Foundation!)
adders

X Y Cin S Cout

0 0 0 0 0

0 0 1 1 0

0 1 0 1 0

0 1 1 0 1

1 0 0 1 0

1 0 1 0 1

1 1 0 0 1

1 1 1 1 1

Adders
  • Basic building block is “full adder”
    • 1-bit-wide adder, produces sum and carry outputs
  • Truth table:
ripple adder
Ripple adder
  • Speed limited by carry chain
  • Faster adders eliminate or limit carry chain
    • 2-level AND-OR logic ==> 2n product terms
    • 3 or 4 levels of logic, carry lookahead
74x283 4 bit adder
74x2834-bit adder
  • Uses carry lookahead internally
slide10

“generate”

“half sum”

carry-in from previous stage

“propagate”

addition in abel
Addition in ABEL
  • Easy?
    • No -- huge number of product terms!
    • On the order of 2n for bit n
    • @CARRY directive
subtraction
Subtraction
  • Subtraction is the same as addition of the two’s complement.
  • The two’s complement is the bit-by-bit complement plus 1.
  • Therefore, X – Y = X + Y + 1 .
    • Complement Y inputs to adder, set Cin to 1.
    • For a borrow, set Cin to 0.
multipliers
Multipliers
  • 8x8 multiplier
why rom
Why “ROM”?
  • Program storage
    • Boot ROM for personal computers
    • Complete application storage for embedded systems.
  • Actually, a ROM is a combinational circuit, basically a truth-table lookup.
    • Can perform any combinational logic function
    • Address inputs = function inputs
    • Data outputs = function outputs
internal rom structure
Internal ROM structure

PDP-11 boot ROM

(64 words, 1024 diodes)

today s roms
Today’s ROMs
  • 256K bytes, 1M byte, or larger
  • Use MOS transistors
eeproms flash proms
EEPROMs, Flash PROMs
  • Programmable and erasableusing floating-gate MOS transistors
eeprom programming
EEPROM programming
  • Apply a higher voltage to force bit change
    • E.g., VPP = 12 V
    • On-chip high-voltage “charge pump” in newer chips
  • Erase bits
    • Byte-byte
    • Entire chip (“flash”)
    • One block (typically 32K - 66K bytes) at a time
  • Programming and erasing are a lot slower than reading (milliseconds vs. 10’s of nanoseconds)
next time
Next time
  • Sequential circuits (Chapter 7)
ad