IEEE 91a-1991 pdf free.IEEE Standard Graphic Symbols for Logic Functions.
IEEE 91a A symbol comprises an outline or combination of outlines together with one or more qualifying symbols.Applicationof the symbols requires, in addi tion, the representation of input and output lines.
Symbols often makeuse of internal labels. lt isessential to maintain clarity betweeninternal labels that apply to signallines and internal labels that serve as general qual ifying symbols.
Labels shal be clearly separated, both horizontally and vertically, from each other and from other symbols or parts ofthe outlinewith which they aenot meant to be associated.Signal-linelabels shal also beplaced such that they are notlikely to be interpreted as general qualifying symbols.
The preferred location for the general qualifying symbol is in the top of the element to which it applies, centeredhorizontally.An alternative position is centered vertically and horizontally.Application of these positioning rules forthe general qualifying symbols should take into account the positions of embedded eements or labels associated withsignal lines that alter the horizontal area available for placement of the general qualifying symbol.
Labels associated with signal lines shall be centered vertically next to those lines. Horizontally, there shal be aspacebetween the signal-line label and the outline of the symbol or symbols atached to the outline.This horizontal spaceshall belarge enough to allow a distinct separation, yet smal enough to unambiguously associate the label with thegiven input or output.
See Appendix A for recommended proportions of symbols and IEEE Sid 991 for more detailed recommendations onsizes and spacing.Because of limitationsin the publishing systems used, symbolsin this document do not always follow the precedingrecommendations.General aditional information may be included in a symbol outline as permitted by an applicable standard forpreparation of diagrams (for example,lEC Publication 111-3 clause 3.4).For supplementary information relating to the function of a complex logic element, see Section 6.In some figures, lowercaseletters that are not part of the symbols have been shown outside the outlinejut to identifythe inputs and outputs as ref erenced in the description.
Information not standardized in this standard relating to a specific input (output) may be shown in square bracketsinside the outline adjacent to the reevant input (output) and should follow(precede) any qualifying symbols applyingto the input (output), as shown in Symbol 5.13-17.IEEE 91a pdf download.