IEEE 991 : 1986

LOGIC CIRCUIT DIAGRAMS, STANDARD FOR

Institute of Electrical & Electronics Engineers

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1. Introduction
1.1 Purpose
1.2 Scope
2. Applicable Documents
2.1 Industry Standards - American National Standards
2.2 Military Standards
2.3 International Standards
3. Definitions
4. General Requirements
4.1 Content
4.1.1 Basic Logic Diagram
4.1.2 Detailed Logic Diagram
4.1.3 Combined Forms of Circuit Diagrams
4.2 Drawing Size and Format
4.2.1 Drawing Zones
4.2.2 Supplemental Drawing Number Location
4.3 Diagram Titles
4.4 Diagram Revisions
4.5 Lettering
4.6 Lines
4.7 Abbreviations
4.8 Letter Symbols
4.9 Layout and Presentation
4.9.1 Coverage
4.9.2 Planning
4.9.3 Signal Flow
4.9.4 Layout
4.9.5 Grouping of Symbols
5. Logic Conventions and Polarity Indication
5.1 Relationship between Logic States and Logic Levels
5.2 Single Logic Convention
5.2.1 Positive Logic Convention
5.2.2 Negative Logic Convention
5.3 Direct Polarity Indication
6. Symbols for Devices and Functions
6.1 Standard Symbols
6.1.1 Symbols for Logic Elements
6.1.2 Distributed Connections (Dot-AND, Dot-OR)
6.2 Size
6.3 Orientation
6.3.1 Orientation of Logic Symbol Lettering
6.3.2 Orientation of Qualifying Symbols Derived from
        Characteristic Curves
6.4 Application and Identification Information
6.4.1 Types of Application Information
6.4.1.1 Reference Designation
6.4.1.2 Element Physical Identification
6.4.1.3 Physical Location of Device
6.4.1.4 Functional Use
6.4.1.5 Terminal Identification
6.4.1.6 Other Information
6.4.2 Application Information Placement
6.4.2.1 Logic Symbols
6.4.2.2 Nonlogic Symbols
6.5 Inputs and Outputs with Multiple Functions
6.6 Abbreviated Representation of Symbols
6.6.1 Identical Inputs and Outputs
6.6.2 Arrays of Identical Elements
6.7 Abutment of Symbols
6.8 Detached Representation of Symbols
6.9 Unused Terminals and Elements
6.10 Devices Having a Large Number of Terminals
7. Interconnection of Symbols
7.1 General Requirements
7.2 Line Spacing
7.3 Junctions and Crossovers
7.4 Interrupted Lines
7.5 Grouping of Lines
7.6 Polarity and Negation Matching
7.7 Power Connections
8. Labeling of Connecting Lines
8.1 General
8.2 Names for Logic and Analog Signals
8.2.1 General Requirements
8.2.1.1 Descriptive Requirements
8.2.1.2 Recommended Characters
8.2.1.3 Length
8.2.1.4 Similar and Equivalent Signals
8.2.2 Binary Logic Signals
8.2.2.1 Signal State
8.2.2.1.1 Negated Signals
8.2.2.1.2 Arithmetic and Logical Expressions
8.2.2.1.3 Bus Signals and Other Grouped Signals
8.2.2.1.4 Clock Signals
8.2.2.2 Signal Level
8.2.3 Analog Signals
8.3 Names for Power and Other Constant-Level Connections
8.4 Locator Information
8.4.1 Cross-Reference Information
8.4.2 Physical Access Information
8.5 Additional Properties and Characterization
9. Supplementary Information
9.1 Reference-Designation Accounting
9.2 Diagram Notes
9.2.1 General Notes
9.2.2 Local Notes
9.2.3 Referenced (Indexed) Notes
9.2.4 Examples
9.3 Tabular Information
9.4 Waveforms
9.4.1 Use
9.4.2 Stylized Waveforms
9.4.3 Simplified Waveform Notations
9.5 Diagram Simplification and Abbreviation Techniques
9.5.1 Repeated Symbol Simplification
9.5.2 Repeated Circuit Patterns
9.5.3 Connections Paired with Ground
9.5.4 Circuit Layout Condensation
10. Examples of Logic Diagrams
FIGURES
1. Line Conventions for Diagrams
2. Distributed Connections
3. Distributed Connections with a Mix of Negated and
      Unnegated Outputs (Positive Logic Shown)
4. Distributed connections with a Mix of Active-High
      and Active-Low Outputs
5. Enlargement of Symbol Outline to Accommodate
      Application Information
6. Logic Symbol Orientation Examples for Diagrams that
      Permit Two Orientations of Text
7. Orientation of Qualifying Symbols Derived from
      Characteristic Curves
8. Application Information: Typical Examples
9. Multiple-Function Terminal (Terminal 1) Shown as
      Separate Lines
10. Multiple-Function Terminal (Terminal 1) Shown as
      a Single Line
11. Multiple-Function Terminal (Terminal 1) Repeated
      on Symbol Outline
12. Abbreviated Representation of Identical Inputs and
      Outputs
13. Abbreviated Representations of Arrays of Identical
      Elements
14. Abutment of Symbols
15. Detached Representations of Devices
16. Diagram Layout
17. Junctions and Crossovers
18. Layout Techniques
19. Grouping of Lines
20. Examples of Signal Name Allocation
21. Clock and Timing Pulses
22. Typical Table Indicating Omitted and Highest
      Numerical Reference Designations
23. Stylized Waveforms
24. Typical Waveforms for Signal Lines
25. Simplified Waveform Notations
26. Repeated Symbol Simplification
27. Typical Diagram Sheet with Repeated Circuit Pattern
28. Single Line Representation of Connections that
      are Paired with Ground
29. Example of Circuit Layout Condensation
30. Basic Logic Diagram for a Timing-Pulse Generator
31. Detailed Logic Diagram - Using the Positive Logic
      Convention
32. Detailed Logic Diagram - Using Direct Polarity
      Indication
33. Typical Circuit Diagram (Direct Polarity Indication)
34. Typical Circuit Diagram (Positive Logic Convention)
TABLES
1. Relationships Among States and Signal Names (Single
      Logic Convention
2. Relationships Among States, Levels, and Signal Names
      (Direct Polarity Indication)
APPENDIXES
A. Mnemonics for Signal Names
B. Lines and Lettering - Size and Spacing
B1. Introduction
B2. Basic Dimensional Relationships
B3. Planning Documents for Multiple Use
C. Single Orientation of Lettering
APPENDIX FIGURES
B1. Minimum Spacing Between Parallel Lines
B2. Lettering Size
B3. Spacing for Lines Surrounding Lettering
B4. Image Area On an Original Document
C1. Logic Symbol Orientation Examples for Diagrams
      that Permit Only One Orientation of Text
APPENDIX TABLES
A1. Signal Names - Alphabetically by Mnemonic
A2. Signal Names - Alphabetically by Meaning
B1. Basic Dimensional Relationships
B2. Minimum Dimensions
B3. Dimensions with Convenient Units for Lettering
      Height (Hc)
B4. Dimensions with Convenient Units for Lettering
      Thickness (Tc)
B5. Determining Image Areas and Reduction Ratios
B6. Multiple-Use Examples Showing Original Lettering
      Thickness (Tc)
B7. Multiple-Use Examples Showing Original Lettering
      Height (Hc)

Abstract

Describes guidelines for preparation of diagrams showing logic functions, including definitions, requirements for assignment of logic levels, application of logic symbols, presentation techniques, and labeling requirement for electrical/electronic systems, but also may be applied to non-electrical systems.