Microsoft Word - Digital Logic Design v_4_6a

 Benefits of PLDs over individual gates:

• Shorter design time (rapid prototype).


• Allow for rapid design changes.


• Decreased PC board real estate.


• Improved reliability since they require fewer packages and interconnections.

 Signal Polarity Convention
There are two types of convention: Positive Logic Convention (PLC) and Direct Polarity Indication
(DPI). It is recommended that polarity be consistent unless there is a practical reason to change
polarity.

 Positive Logic Convention (PLC)

• Other name for PLC: True Form.


• PLC has been used so far and we will continue to use it in the rest of the text. It is best
  suited for working with logic (ones and zeros).

 Direct Polarity Indication (DPI)

• Other name for DPI: Complemented Form.


• DPI is also referred to as the mixed signal since each signal can have polarity attached to it
  For example W(H) is W in positive logic which is the same as W L)(


• DPI is preferred by engineers who need to be aware of voltage levels correlating with the
  active levels


• Here is a comparison of DPI and PLC signal naming

PLC Signal Name DPI signal Name Type of Signal

A A(H) or AL)( Active High

A A(H)or A(L) Active Low

Use bubble “o” to indicate

negation

Use wedge to indicate

polarity (Low)

Write signal name with no

over bar and change to

Active low with polarity

indicator.

(1) Double complementation can be used to write equivalent signal names in a number of

formats

A 1 ... A 0

p 0

p 1

OE0

Fuse Map

F(A 0 ,A 1 )