Logic gate diagram

Dual-standard support: IEEE Std 91-1984/91a-1991 (ANSI distinctive shapes) + IEC 60617-12 (rectangular symbols).

Primary References:

• IEEE Std 91-1984 / ANSI Y32.14: Logic Symbol Standard (Distinctive-Shape)
• IEEE Std 91a-1991: Supplement for distinctive-shape symbols
• IEC 60617-12: Graphical symbols for diagrams — binary logic elements
• Schemdraw Logic module: https://schemdraw.readthedocs.io/en/stable/classes/logic.html

1. Gate Symbol Set

1.1 Symbol Style Options

Both standards are supported; Schematex selects between them via the render config style parameter:

1.2 Combinational Gate Symbols (ANSI Distinctive Shape)

All coordinates are based on a 100×60px normalized space (width×height), scalable via the scale parameter.

AND Gate

• Shape: Flat back (left) + semicircle front (right), D-shape
• SVG Path: M 20,60 L 20,0 Q 80,0 80,30 Q 80,60 20,60 Z
• Input Pin 1: (20, 15) — left edge, upper
• Input Pin 2: (20, 45) — left edge, lower
• Output Pin: (80, 30) — right center
• Wire extension: inputs extend 10px left, output extends 10px right
• IEC Symbol: Rectangle (10,5)→(90,55) + centered & label

OR Gate

• Shape: Curved back (left) + pointed front (right), crescent shape
• SVG Path: M 15,60 Q 10,30 15,0 Q 30,15 70,30 Q 30,45 15,60 Z
• Input Pin 1: (15, 15) — curved left, upper
• Input Pin 2: (15, 45) — curved left, lower
• Output Pin: (70, 30) — right point
• IEC Symbol: Rectangle + ≥1 label

NOT Gate (Inverter)

• Shape: Triangle + output bubble circle
• SVG Path: M 10,55 L 55,30 L 10,5 Z (triangle)
• Bubble: <circle cx="60" cy="30" r="5"/>
• Input Pin: (10, 30) — left
• Output Pin: (65, 30) — after bubble
• IEC Symbol: Rectangle + 1 label + output bubble circle

NAND Gate

• AND Gate shape + output bubble
• Output Pin: (85, 30) (AND output + bubble radius 5)
• IEC Symbol: Rectangle + & + output bubble

NOR Gate

• OR Gate shape + output bubble
• Output Pin: (75, 30) (OR output + bubble radius 5)
• IEC Symbol: Rectangle + ≥1 + output bubble

XOR Gate

• OR Gate + extra curved back line (parallel to back curve)
• Extra path: M 8,60 Q 3,30 8,0 (parallel arc, offset 7px left of OR back)
• Input Pin 1: (8, 15) — from extra arc
• Input Pin 2: (8, 45) — from extra arc
• Output Pin: (70, 30) — same as OR
• IEC Symbol: Rectangle + =1

XNOR Gate

• XOR Gate + output bubble
• IEC Symbol: Rectangle + =1 + output bubble

Buffer (Non-inverting)

• Triangle (no bubble)
• SVG Path: M 10,55 L 55,30 L 10,5 Z
• Input Pin: (10, 30), Output Pin: (55, 30)
• IEC Symbol: Rectangle + 1 (no bubble)

Tri-State Buffer

• Buffer + enable input (bottom control line)
• Enable Input Pin: (30, 55) — bottom center
• When enable = 0, output is Z (high-impedance)

1.3 3-Input Gate Variants

The 3-input variant adds a third pin at center height:

• AND3 Pin 3: (20, 30) — left edge, center
• OR3 Pin 3: (15, 30) — curved left, center
• 4-input follows the same pattern (evenly distributed along the left edge)

1.4 Bubble (Active-Low) Notation

Input bubble = active-low input; the circle is placed between the pin and the gate body:

<circle cx="x_pin_end" cy="y_pin" r="4" fill="white" stroke="#333" stroke-width="1.5"/>

The input pin extends an extra 8px (bubble diameter); the wire enters from (x_pin_end - 4, y_pin).

1.5 Clock Input Triangle

In flip-flop elements, the clock input is marked with a small triangle:

<!-- Triangle pointing right, at clock pin position (x_clk, y_clk) -->
<polygon points="x_clk,y_clk-5 x_clk+8,y_clk x_clk,y_clk+5"
         fill="#333" stroke="none"/>

2. Sequential Logic Symbols

2.1 D Flip-Flop

Rectangle box (0,0)→(60,80) + the following pins:

Clock triangle SVG (on the left side of the box, at CLK pin position):

<polygon points="0,35 8,40 0,45" fill="#333"/>

Q̄ bubble (on the right side of the box, at Q̄ pin position):

<circle cx="64" cy="60" r="4" fill="white" stroke="#333" stroke-width="1.5"/>

2.2 JK Flip-Flop

Rectangle box (0,0)→(60,80) + the following pins:

2.3 SR Latch (no clock)

Rectangle box (0,0)→(50,60) + pins:

2.4 T Flip-Flop

Rectangle box (0,0)→(60,60):

2.5 Register (N-bit)

Larger rectangle box, height scales with bit width:

• Input bus: left side, with /N bus annotation
• CLK: left side, triangle marker
• Output bus: right side, with /N annotation
• Bus lines use thick stroke (stroke-width: 3) + slash annotation for bit width

3. Connection & Wiring Conventions

3.1 Wire Routing

• Orthogonal routing (Manhattan routing): all wires are horizontal or vertical, never diagonal
• Signal flow direction: left → right (inputs on the left, outputs on the right)
• Feedback paths: routed above or below the main signal flow

3.2 Junction & Crossing

<!-- Junction dot at (x, y) -->
<circle cx="x" cy="y" r="3" fill="#333" class="lt-junction"/>

<!-- Bridge: bottom line has gap at crossing -->
<!-- 1. Draw bottom line with gap (two segments) -->
<line x1="x1" y1="y" x2="x_cross-5" y2="y" stroke="#333" stroke-width="2"/>
<line x1="x_cross+5" y1="y" x2="x2" y2="y" stroke="#333" stroke-width="2"/>
<!-- 2. Draw top line continuously -->
<line x1="x" y1="y1" x2="x" y2="y2" stroke="#333" stroke-width="2"/>

3.3 Bus Notation

Multi-bit buses use thick lines + slash annotation:

<!-- Bus line (thick) -->
<line x1="x1" y1="y" x2="x2" y2="y" stroke="#333" stroke-width="4"/>
<!-- Bit-width annotation slash + text -->
<line x1="x_mid-6" y1="y+8" x2="x_mid+6" y2="y-8" stroke="#333" stroke-width="1.5"/>
<text x="x_mid+8" y="y-6" font-size="9">8</text>

3.4 Signal Labels on Wires

Wire labels are placed 5px above the midpoint of the wire segment:

<text x="x_mid" y="y_wire-6" font-size="10" text-anchor="middle"
      class="lt-wire-label">SIGNAL_NAME</text>

3.5 Power Symbols

<!-- VCC (power, pointing up) -->
<polygon points="x,y x-6,y+10 x+6,y+10" fill="#333"/>
<text x="x" y="y+20" font-size="9" text-anchor="middle">VCC</text>

<!-- GND (ground, pointing down) -->
<line x1="x" y1="y" x2="x" y2="y+10" stroke="#333" stroke-width="2"/>
<line x1="x-10" y1="y+10" x2="x+10" y2="y+10" stroke="#333" stroke-width="2"/>
<line x1="x-6" y1="y+14" x2="x+6" y2="y+14" stroke="#333" stroke-width="2"/>
<line x1="x-2" y1="y+18" x2="x+2" y2="y+18" stroke="#333" stroke-width="2"/>

4. Layout Conventions

4.1 Signal Flow Direction

• Primary axis: left → right (inputs at the far left, outputs at the far right)
• Vertical axis: signals arranged by logic depth (inputs above/below, outputs in the middle)
• Feedback: routed above or below the main signal path, without overlapping it

4.2 Gate Placement

• Horizontal spacing: center-to-center distance between adjacent gates ≥ 120px (100px gate + 20px wire)
• Vertical spacing: center-to-center distance between adjacent gates ≥ 80px
• Depth alignment: gates at the same logic depth are aligned in the same vertical column

4.3 Layout Algorithm (DAG-based)

Logic gate diagram layout is a DAG (directed acyclic graph) topological sort problem:

1. Topological sort: layer by signal dependency (depth = layer index)
2. Layer assignment: each gate is assigned to its maximum depth layer (critical path)
3. Vertical arrangement: gates in the same layer are arranged top to bottom, evenly spaced
4. Coordinate assignment: x = layer × 120 + name_column_width, y = position_in_layer × 80
5. Wire routing: Manhattan routing, routed around gate boundaries

4.4 Label Positioning

• Gate type labels (e.g., AND, OR): centered inside the gate, 10px sans-serif
• Pin labels (D, J, K, Q): beside the pin, 9px, 5px from pin
• Wire labels: 6px above the midpoint of the wire segment, 10px, centered

5. DSL Grammar (Logic Gate Diagram)

document    = header statement*
header      = "logic" quoted_string? props? NEWLINE
props       = "[" prop ("," prop)* "]"
prop        = "style:" ("ansi" | "iec")
            | "scale:" FLOAT

statement   = comment | input_def | output_def | gate_def | wire_def

comment     = "#" [^\n]* NEWLINE

input_def   = "input" id_list NEWLINE
id_list     = IDENTIFIER ("," IDENTIFIER)*

output_def  = "output" id_list NEWLINE

gate_def    = IDENTIFIER "=" gate_type "(" input_list ")" NEWLINE
gate_type   = "and" | "or" | "not" | "nand" | "nor" | "xor" | "xnor"
            | "buf" | "tri"
            | "and3" | "or3" | "and4" | "or4"
            | "dff" | "jkff" | "srff" | "tff"
gate_type_3 = "and3" | "or3" | "nand3" | "nor3" | "xor3"
input_list  = (IDENTIFIER | neg_input) ("," (IDENTIFIER | neg_input))*
neg_input   = "~" IDENTIFIER    # active-low / inverted input

wire_def    = IDENTIFIER "->" IDENTIFIER label_clause? NEWLINE
            | IDENTIFIER "~>" IDENTIFIER label_clause?  # bus connection
label_clause = "[" quoted_string "]"

IDENTIFIER  = /[a-zA-Z][a-zA-Z0-9_]*/
FLOAT       = /[0-9]+(\.[0-9]+)?/
INT         = /[0-9]+/
quoted_string = '"' /[^"]*/ '"'
NEWLINE     = /\n/

DSL Example (Full Adder):

logic "1-bit Full Adder" [style: ansi]

input A, B, Cin
output Sum, Cout

# First XOR for sum intermediate
s1 = xor(A, B)

# Second XOR for final sum
Sum = xor(s1, Cin)

# AND gates for carry
c1 = and(A, B)
c2 = and(s1, Cin)

# OR for carry out
Cout = or(c1, c2)

DSL Example (D Flip-Flop with enable):

logic "D FF with Enable"

input D, CLK, EN
output Q

# Gate-level enable logic
d_in = and(D, EN)
Q = dff(d_in, CLK)

6. SVG Structure

<svg class="lt-logic" data-diagram-type="logic">
  <defs>
    <style>
      .lt-gate-body  { fill: white; stroke: #333; stroke-width: 2; }
      .lt-gate-label { font: bold 10px sans-serif; fill: #333; }
      .lt-pin-label  { font: 9px sans-serif; fill: #555; }
      .lt-wire       { stroke: #333; stroke-width: 2; fill: none; }
      .lt-bus        { stroke: #333; stroke-width: 4; fill: none; }
      .lt-wire-label { font: 10px sans-serif; fill: #333; }
      .lt-junction   { fill: #333; }
      .lt-bubble     { fill: white; stroke: #333; stroke-width: 1.5; }
      .lt-clock-tri  { fill: #333; }
    </style>
    <!-- Arrowhead for signal direction (optional) -->
    <marker id="lt-logic-arrow" markerWidth="6" markerHeight="6"
            refX="5" refY="3" orient="auto">
      <polygon points="0 0, 6 3, 0 6" fill="#333"/>
    </marker>
  </defs>
  <title>Logic Gate Diagram — [name]</title>
  <desc>[description]</desc>

  <!-- Gates -->
  <g id="lt-gates">
    <g id="gate-AND1" data-type="and" data-id="AND1" transform="translate(x, y)">
      <path class="lt-gate-body" d="..."/>
      <!-- pin wires -->
      <line class="lt-wire" .../>
    </g>
  </g>

  <!-- Wires -->
  <g id="lt-wires">
    <path class="lt-wire" d="M x1,y1 L x_bend,y1 L x_bend,y2 L x2,y2" .../>
  </g>

  <!-- Labels -->
  <g id="lt-labels">...</g>

  <!-- Junctions -->
  <g id="lt-junctions">
    <circle class="lt-junction" cx="x" cy="y" r="3"
            data-signals="A,B" />
  </g>
</svg>

7. Test Cases

Case 1: Simple AND Gate

logic
input A, B
output Y
Y = and(A, B)

Verify: AND gate is centered, two input wires from the left, output wire to the right, coordinates correct.

Case 2: Half Adder

logic "Half Adder"
input A, B
output S, C
S = xor(A, B)
C = and(A, B)

Verify: XOR and AND are side by side, both sharing inputs A and B (with junction dots).

Case 3: Full Adder

logic "Full Adder"
input A, B, Cin
output Sum, Cout
s1 = xor(A, B)
Sum = xor(s1, Cin)
c1 = and(A, B)
c2 = and(s1, Cin)
Cout = or(c1, c2)

Verify: 5 gates, signal reuse correct, s1 fans out to two gates (junction dot).

Case 4: D Flip-Flop

logic
input D, CLK
output Q
Q = dff(D, CLK)

Verify: DFF rectangle box renders correctly, clock triangle at CLK pin, Q̄ has a bubble.

Case 5: IEC Style

logic [style: iec]
input A, B
output Y
Y = nand(A, B)

Verify: NAND gate renders as rectangle + "&" label + output bubble (IEC style).

Case 6: Active-Low Input

logic
input A, ~B
output Y
Y = and(A, ~B)

Verify: input B has a bubble at the input pin, wire enters from the left of the bubble.

8. Implementation Priority

6. Extended Symbol Library (v2): Special Buffers, Latches & Complex Elements

The following extends the v1 standard, covering variants frequently used in real engineering digital circuits. All symbols follow IEEE Std 91-1984 ANSI style (ANSI primary; IEC equivalents given in parentheses).

6.1 Tri-State Buffer (TRISTATE_BUF)

• IEEE 91 description: Buffer with control input (EN/OE); output = Z (high-impedance) when disabled
• Pins: A (data in), EN (enable, active-high), Y (output)
• Active-low enable: add bubble at EN pin → ~EN
• ANSI symbol: Buffer triangle + extra enable pin entering from the bottom

  /* Buffer triangle (same as BUF) */
  M 0,20 V 40  M 0,40 L 35,30 L 0,20  /* triangle body */
  M -20,30 H 0   /* data input A */
  M 35,30 H 55   /* output Y */
  /* Enable input from below */
  M 15,50 V 36   /* EN pin wire */
  /* EN label at (15, 55) */

• IEC symbol: Rectangle body with "EN" label and "1" function designation
• Output Z-state indicator: renderer sets data-tristate="true", shown as a dashed output line

6.2 Tri-State Inverter (TRISTATE_INV)

• Pins: A (data in), EN (enable), Y (inverted output)
• ANSI symbol: NOT triangle + bubble at output + enable pin

  /* NOT triangle body */
  M 0,20 V 40  M 0,40 L 35,30 L 0,20
  /* inversion bubble */
  <circle cx="38" cy="30" r="4" fill="white" stroke-width="1.5"/>
  /* EN pin from below at body midpoint */
  M 12,50 V 36

6.3 Open-Drain Buffer (OPEN_DRAIN)

• Description: Output transistor pulls to GND when active; high state requires external pull-up
• Pins: A (input), Y (open-drain output)
• ANSI symbol: Buffer triangle + special output symbol (triangle pointing toward GND)

  /* Buffer triangle */
  M 0,20 V 40  M 0,40 L 30,30 L 0,20
  /* Open-drain indicator: downward triangle at output */
  M 30,30 L 42,24 L 42,36 Z   fill="none" stroke-width="1.5"
  /* implied: external pull-up resistor on output line */

• Note: when the [pullup: "10k"] attr is set in DSL, the renderer additionally draws a pull-up resistor symbol

6.4 Schmitt Trigger (SCHMITT)

• IEEE 91 description: Hysteresis symbol (square-wave shape) inside buffer triangle
• Pins: A (input), Y (output)
• ANSI symbol: Buffer triangle + hysteresis square-wave symbol (small S-shape)

  /* Buffer triangle */
  M 0,20 V 40  M 0,40 L 35,30 L 0,20
  /* Hysteresis symbol inside at (15, 30): miniature square-wave hysteresis curve */
  M 10,32 H 14 V 28 H 18 V 32 H 22   /* step symbol */
  /* input/output wires */
  M -20,30 H 0
  M 35,30 H 55

• Inverting variant: add bubble at the output

6.5 SR Latch (LATCH_SR)

• IEEE 91 description: Level-sensitive (not clocked), no clock pin. Set/Reset asynchronous.
• Distinction from SRFF: no clock triangle; responds directly to S/R levels
• Pins: S (set), R (reset), Q, ~Q
• ANSI symbol: Rectangle 60×60px + S/R left, Q/~Q right, no clock

  M 0,0 H 60 V 60 H 0 Z   /* body */
  /* Inputs on left */
  M -20,15 H 0   /* S pin */
  M -20,45 H 0   /* R pin */
  /* Outputs on right */
  M 60,15 H 80   /* Q pin */
  M 60,45 H 80   /* ~Q pin */
  /* bubble on ~Q output */
  <circle cx="63" cy="45" r="4" fill="white" stroke-width="1.5"/>
  /* Pin labels: "S" (5,14), "R" (5,44), "Q" (52,14), "Q̄" (52,44) */

• IEC symbol: Same rect with "SR" inside

6.6 D Latch (LATCH_D)

• IEEE 91 description: Level-sensitive (transparent when E=1); edge-triggered version = DFF
• Pins: D (data), E or EN (enable/gate), Q, ~Q
• ANSI symbol: DFF-style rectangle but without clock triangle

  M 0,0 H 60 V 60 H 0 Z   /* body */
  /* D input (left top) */
  M -20,15 H 0
  /* E input (left bottom) */
  M -20,45 H 0
  /* NO clock triangle (key distinction from DFF — this is the D Latch) */
  /* Outputs right */
  M 60,15 H 80   /* Q */
  M 60,45 H 80   /* ~Q + bubble */
  /* Pin labels: "D", "E", "Q", "Q̄" */

• Note: when DSL writes G3 = LATCH_D(D=A, E=CLK_EN), no clock triangle is drawn

6.7 Counter (COUNTER)

• IEEE 91 description: Binary counter, generic representation
• Pins: CLK, RESET/CLR (inputs); Q0, Q1, Q2, Q3 (outputs)
• Optional pins: EN (enable), LOAD (parallel load), D0–D3 (preset data), CO (carry out)
• ANSI symbol: Larger rectangle (60×80px) + "CTR" label

  M 0,0 H 60 V 80 H 0 Z   /* body */
  /* CLK input (left, with clock triangle) */
  M -20,25 H 0
  <polygon points="0,20 8,25 0,30"/>   /* clock triangle */
  /* CLR input */
  M -20,55 H 0
  /* Q outputs (right): Q0 at y=15, Q1 at y=30, Q2 at y=45, Q3 at y=60 */
  M 60,15 H 80   M 60,30 H 80   M 60,45 H 80   M 60,60 H 80
  /* CO (carry out) at right bottom */
  M 60,72 H 80
  /* "CTR" label centered in body */
  /* Pin labels: CLK, CLR, Q0-Q3, CO */

• attrs in DSL: [bits: 4] (default 4), [mode: up|down|updown]

6.8 Shift Register (SHIFT_REG)

• IEEE 91 description: Generic shift register, serial or parallel I/O
• Pins: CLK, SER (serial in), SHIFT/LOAD, Q0–Q7 (parallel out), SER_OUT (serial out)
• ANSI symbol: Large rectangle (60×100px) + "SRG" label

  M 0,0 H 60 V 100 H 0 Z   /* body */
  /* CLK (left, clock triangle) */
  M -20,20 H 0
  <polygon points="0,15 8,20 0,25"/>
  /* SER in */
  M -20,40 H 0
  /* SHIFT/LOAD control */
  M -20,60 H 0
  /* Q0-Q7 outputs on right (8 outputs, 10px spacing) */
  /* SER_OUT at bottom-right */
  /* "SRG" label in body */
  /* attrs: [bits: 8], [mode: SIPO|PISO|PIPO] */

6.9 Pin Annotation: Active-Low and Edge-Triggered Notation

6.10 Updated Implementation Priority (v2)

Total logic gate symbols (v2): 24 (P0: 16, P1: 6, P2: 2)