EE101Lecture16

EE101Lecture16 - Mark Redekopp, All rights reserved...

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Unformatted text preview: Mark Redekopp, All rights reserved Introduction to Digital Logic Lecture 16: ROMs Tri-States Combinational vs. Sequential Logic Mark Redekopp, All rights reserved Memories Memories store (write) and retrieve (read) data Read- Only Memories (ROMs): Can only retrieve data (contents are initialized and then cannot be changed) Read- Write Memories (RWMs): Can retrieve data and change the contents to store new data Mark Redekopp, All rights reserved ROMs 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 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A 2 A A 1 D 3 D 2 D 1 D 1 2 3 4 5 6 7 Address Inputs Data Outputs ROM Mark Redekopp, All rights reserved ROMs 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 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 A 2 A A 1 1 1 1 1 2 3 4 5 6 7 Address: 100 2 = 4 10 Data: Row 4 is output ROM 1 D 3 D 2 D 1 D Mark Redekopp, All rights reserved ROMs ROMs 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 1 1 1 2 2 n-2 ROM . . . 2 n-1 A n-1 A A 1 D m-1 D Mark Redekopp, All rights reserved ROMs One major application of ROMs is to use them as LUTs (Look-Up Tables) 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 Mark Redekopp, All rights reserved Implementing Functions w/ ROMs 1 1 1 1 A 2 A A 1 D 1 2 3 4 5 6 7 8x1 ROM X Y Z F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Arbitrary Logic Function X Z Y F 1 1 1 1 A 2 A A 1 D 1 2 3 4 5 6 7 8x1 ROM 1 1 X,Y,Z inputs X,Y,Z inputs look up the correct answer Mark Redekopp, All rights reserved...
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EE101Lecture16 - Mark Redekopp, All rights reserved...

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