# CH9B - Programmable Logic g g Devices (c) Hasan Zidan...

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Programmable Logic Devices (c) Hasan Zidan Department of Electrical Engineering AUST 1

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Programmable Logic Other ways to implement a logic function than to hook together discrete 74XX packages or create a custom I ntegrated C ircuit. 1. One can use semiconductor MEMORY to implement ogic (Functions) equations Logic (Functions) equations. 2. One can use I ntegrated C ircuits known as “Programmable Logic Devices” to implement Logic Functions. 2
Memory We think of a memory device as used for storing data only. Memory chip is characterized by how many locations it contains and how many bits per location it can hold. Memories are classified as K x M devices, K is the No. of locations, M is the No. bits per location (16 x 2 would be 16 t i h t i it ) locations, each storing 2 bits). To access a LOCATION within a memory device, a group of puts known as the DDRESS BUS re used The number of inputs known as the ADDRESS BUS are used. The number of address lines needed for 16 locations would be 4 address lines. he data at a location is placed on some outputs known as 3 The data at a location is placed on some outputs known as the DATA bus.

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Memory Examples 2 emory ( 2 cations, [ 32 x 8 32 x 8 memory (32 locations, 8 bits per location), total of storing capacity of 256 bits. A[4:0] D[7:0] 4 emor ( 4 cations Needs 5 address lines, 8 data lines 5 8 64 x 2 64 x 2 memory (64 locations , 2 bits per location ). eeds ddress nes ata A[5:0] D[1:0] Needs 6 address lines, 2 data lines 6 2 4
Look Up Table (LUT) Loc A B C D F(A,B,C,D) 0 0 0 0 0 0 1 0 0 0 1 0 memory device can be 2 0 0 1 0 1 3 0 0 1 1 1 4 0 1 0 0 0 A memory device can be thought of as a LookUp Table (LUT), in which each t i t i 5 0 1 0 1 0 6 0 1 1 0 1 7 0 1 1 1 0 1000 0 location contains 1 or more bits. 16 x 1 Memory 8 1 0 0 0 0 9 1 0 0 1 0 10 1 0 1 0 1 1011 0 A B A3 O F A2 11 1 0 1 1 0 12 1 1 0 0 0 13 1 1 0 1 1 14 1 1 1 0 1 C D A1 A0 5 15 1 1 1 1 1

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ROM Implementation of Boolean Functions Contents of ROM usually specified by a truth table n OM A 2 x m ROM can realize m functions of n variables Decoder 6 generates all minterms of input variables Switching elements effectively form an OR gate e.g. F 0 = m 0 +m 1 + m 4 + m 6
Example: Code Converter ± Truth table: BCD Excess-3 AB C DWXYZ 0 0 0 0 0 0 0 1 1 1 0 0 0 1 0 1 0 0 2 0 0 1 0 0 1 0 1 3 0 0 1 1 0 1 1 0 4 0 1 0 0 0 1 1 1 5 0 1 0 1 1 0 0 0 6 0 1 1 0 1 0 0 1 7 0 1 1 1 1 0 1 0 8 1 0 0 0 1 0 1 1 9 1 0 0 1 1 1 0 0 10 1 0 1 0 X X X X 11 1 0 1 1 X X X X 12 1 1 0 0 X X X X 13 1 1 0 1 X X X X

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## This note was uploaded on 03/10/2012 for the course ENGINEERIN 131231 taught by Professor Dr.hamad during the Spring '12 term at Amity University.

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CH9B - Programmable Logic g g Devices (c) Hasan Zidan...

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