EE101Lecture16

EE101Lecture16 - Introduction to Digital Logic Lecture 16:...

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© Mark Redekopp, All rights reserved Introduction to Digital Logic Lecture 16: ROM’s Tri-States Combinational vs. Sequential Logic
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© Mark Redekopp, All rights reserved Memories • Memories store (write) and retrieve (read) data – Read-Only Memories (ROM’s): Can only retrieve data (contents are initialized and then cannot be changed) – Read-Write Memories (RWM’s): Can retrieve data and change the contents to store new data
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© Mark Redekopp, All rights reserved ROM’s • Memories are just tables of data with rows and columns • When data is read, one entire row of data is read out • The row to be read is selected by putting a binary number on the address inputs 1 1 0 1 0 1 1 0 0 0 0 1 1 0 1 1 1 1 1 0 0 0 1 0 0 1 0 1 1 1 0 0 A 2 A 0 A 1 D 3 D 2 D 1 D 0 0 1 2 3 4 5 6 7 Address Inputs Data Outputs ROM
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© Mark Redekopp, All rights reserved ROM’s • Memories are just tables of data with rows and columns • When data is read, one entire row of data is read out • The row to be read is selected by putting a binary number on the address inputs 1 1 0 1 0 1 1 0 0 0 0 1 1 0 1 1 1 1 1 0 0 0 1 0 0 1 0 1 1 1 0 0 A 2 A 0 A 1 11 01 0 1 2 3 4 5 6 7 Address: 100 2 = 4 10 Data: Row 4 is output ROM 1 0 0 D 3 D 2 D 1 D 0
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© Mark Redekopp, All rights reserved ROM’s • ROM’s are named by their dimensions: – Rows x Columns n rows and m columns => n x m ROM •2 n rows => n address bits (or k rows => log 2 k address bits) • m cols. => m data outputs 1 1 0 0 0 0 0 1 1 0 0 1 2 2 n -2 ROM . . . 2 n -1 A n-1 A 0 A 1 D m-1 D 0
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© Mark Redekopp, All rights reserved ROM’s • One major application of ROM’s is to use them as LUT’s (to implement logic functions) • Given a logic function use a ROM to hold all the possible answers and feed the inputs of the function to the address inputs to look-up the answer
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© Mark Redekopp, All rights reserved Implementing Functions w/ ROM’s 1 0 1 1 0 0 1 0 A 2 A 0 A 1 D 0 0 1 2 3 4 5 6 7 8x1 ROM 0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 1 1 1 1 0 1 0 1 0 0 1 0 0 1 0 0 0 F Z Y X Logic Function X Z Y F 1 0 1 1 0 0 1 0 A 2 A 0 A 1 D 0 0 1 2 3 4 5 6 7 8x1 ROM 1 0 1 0 X,Y,Z inputs “look up” the correct answer X,Y,Z inputs “look up” the correct answer
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© Mark Redekopp, All rights reserved Implementing Functions w/ ROM’s 1 1 1 0 1 0 0 0 1 0 0 1 0 1 1 0 A 2 A 0 A 1 D 1 0 1 2 3 4 5 6 7
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This note was uploaded on 02/27/2008 for the course EE 101 taught by Professor Redekopp during the Fall '06 term at USC.

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EE101Lecture16 - Introduction to Digital Logic Lecture 16:...

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