The Open Source Swiss Army Knife
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complex programmable logic devices and ROM
PAL: programmable array logic
PLA: programmable logic array
a pla performs the same basic function as a ROM. a PLA with n inputs and m
outputs can realize m functions of n variables. The internal structure
differs from that of a ROM because the decoder is replaced by an AND array
which realizes the selected product terms of the input variables. The second
part of the internal structure of a PLA is an OR array which ORs together the
product terms needed to form the output functions.
a PAL is almost the same as a PLA only it has the AND gates fused in at the
factory.
structure: decoder with a memory array
The decoder structure was noted by me in
the contents of a ROM are specified by a truth table. The turth table
specifies the multiple output values for each row of the truth table.
The memory array is a combinations of some of the output lines from the
truth table which generate the true values of the output functions.
has 2(n)m inputs. m* is the rows output. That equation is used to find,
for example question, the number of inputs required to produce a certain
number of outputs.
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