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 3 All minterms can be called product terms but vice versa is not true. edited Oct 6 '17 at 15:40 Peter Green 12.6k11 gold badge2222 silver badges4242 bronze badges We can think of a simple programmable logic device as an array of andAND gates followed by an array of orOR gates (in reality it may actually be implemented as two arrays of NAND gates). In a PROM the "AND array" is fixed and the "OR array" is programmable. Every combination of inputs generates exactly one output from the AND array. The "OR array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitrary logic functions sounds attractive but there are two practical problems to using PROMs for logic. Firstly, it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly, it is very prone to output glitches because the mintermsproduct terms used each cover exactly one input combination. In a PAL the "OR array" is fixed and the "AND array" is programmable. Each output must be formed from a restricted number of product terms but those product terms can each cover multiple input combinations. In a PLA both arrays are programmable. This gives you more flexibility if some outputs need more product terms than others or if several outputs have product terms in common. We can think of a simple programmable logic device as an array of and gates followed by an array of or gates (in reality it may actually be implemented as two arrays of NAND gates). In a PROM the "AND array" is fixed and the "OR array" is programmable. Every combination of inputs generates exactly one output from the AND array. The "OR array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitrary logic functions sounds attractive but there are two practical problems to using PROMs for logic. Firstly, it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly, it is very prone to output glitches because the minterms used cover exactly one input combination. In a PAL the "OR array" is fixed and the "AND array" is programmable. Each output must be formed from a restricted number of product terms but those product terms can each cover multiple input combinations. In a PLA both arrays are programmable. This gives you more flexibility if some outputs need more product terms than others or if several outputs have product terms in common. We can think of a simple programmable logic device as an array of AND gates followed by an array of OR gates (in reality it may actually be implemented as two arrays of NAND gates). In a PROM the "AND array" is fixed and the "OR array" is programmable. Every combination of inputs generates exactly one output from the AND array. The "OR array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitrary logic functions sounds attractive but there are two practical problems to using PROMs for logic. Firstly, it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly, it is very prone to output glitches because the product terms used each cover exactly one input combination. In a PAL the "OR array" is fixed and the "AND array" is programmable. Each output must be formed from a restricted number of product terms but those product terms can each cover multiple input combinations. In a PLA both arrays are programmable. This gives you more flexibility if some outputs need more product terms than others or if several outputs have product terms in common. 2 All minterms can be called product terms but vice versa is not true. edit approved Oct 6 '17 at 15:40 vugoball 322 bronze badges We can think of a simple programableprogrammable logic device as an array of and gates followed by an array of or gates (in reality it may actually be implemented as two arrays of nandNAND gates). In a promPROM the "and"AND array" is fixed and the "or"OR array" is programableprogrammable. Every combination of inputs generates exactly one output from the andAND array. The "or"OR array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitaryarbitrary logic functions sounds attractive but there are two practical problems to using promsPROMs for logic. Firstly, it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly, it is very prone to output glitches because the minterms used cover exactly one input combination. In a PLAPAL the "or"OR array" is fixed and the "and"AND array" is programmable. Each output must be formed from a restricted number of mintermsproduct terms but those mintermsproduct terms can each cover multiple input combinations. In a PALPLA both arrays are programmable. This gives you more flexibility if some outputs need more mintermsproduct terms than others or if several outputs have mintermsproduct terms in common.   We can think of a simple programable logic device as an array of and gates followed by an array of or gates (in reality it may actually be implemented as two arrays of nand gates). In a prom the "and array" is fixed and the "or array" is programable. Every combination of inputs generates exactly one output from the and array. The "or array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitary logic functions sounds attractive but there are two practical problems to using proms for logic. Firstly it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly it is very prone to output glitches because the minterms used cover exactly one input combination. In a PLA the "or array" is fixed and the "and array" is programmable. Each output must be formed from a restricted number of minterms but those minterms can each cover multiple input combinations. In a PAL both arrays are programmable. This gives you more flexibility if some outputs need more minterms than others or if several outputs have minterms in common.   We can think of a simple programmable logic device as an array of and gates followed by an array of or gates (in reality it may actually be implemented as two arrays of NAND gates). In a PROM the "AND array" is fixed and the "OR array" is programmable. Every combination of inputs generates exactly one output from the AND array. The "OR array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitrary logic functions sounds attractive but there are two practical problems to using PROMs for logic. Firstly, it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly, it is very prone to output glitches because the minterms used cover exactly one input combination. In a PAL the "OR array" is fixed and the "AND array" is programmable. Each output must be formed from a restricted number of product terms but those product terms can each cover multiple input combinations. In a PLA both arrays are programmable. This gives you more flexibility if some outputs need more product terms than others or if several outputs have product terms in common. 1 answered Mar 6 '17 at 11:06 Peter Green 12.6k11 gold badge2222 silver badges4242 bronze badges We can think of a simple programable logic device as an array of and gates followed by an array of or gates (in reality it may actually be implemented as two arrays of nand gates). In a prom the "and array" is fixed and the "or array" is programable. Every combination of inputs generates exactly one output from the and array. The "or array" is then programmed to define the logic function. This allows every output to implement any logic function of the inputs. Being able to implement arbitary logic functions sounds attractive but there are two practical problems to using proms for logic. Firstly it doesn't scale well, each extra input you add doubles the required size of the and array. Secondly it is very prone to output glitches because the minterms used cover exactly one input combination. In a PLA the "or array" is fixed and the "and array" is programmable. Each output must be formed from a restricted number of minterms but those minterms can each cover multiple input combinations. In a PAL both arrays are programmable. This gives you more flexibility if some outputs need more minterms than others or if several outputs have minterms in common.