Schematex

Ladder logic

Industrial PLC programs in IEC 61131-3 ladder logic. Allen-Bradley tag+address+description labels, Set/Reset coil pairs, parallel branches, seal-in circuits. For manufacturing and automation.

Line 7: invalid element syntax: branch: OTL(SYS_AUTO, "BIT 3.1", name="System Auto Mode")

IEC 61131-3:2013 梯形图语言规范 + NEMA ICS 1-2009 北美标准。

Primary References:

  • IEC 61131-3:2013 — Programmable controllers, Part 3: Programming languages (Ladder Diagram is one of 5)
  • NEMA ICS 1-2009 — General Standards for Industrial Control and Systems (NA standard)
  • Allen-Bradley (Rockwell) RSLogix / Studio 5000 ladder conventions
  • Siemens TIA Portal ladder conventions

1. Structure & Layout

1.1 Overall Diagram Structure

│ Power Rail L │                                  │ Power Rail R │
│              │                                  │              │
│              ├──[element]──[element]──...────────┤              │ ← Rung 0
│              │                                  │              │
│              ├──[element]──[branch]─────────────┤              │ ← Rung 1
│              │               │                  │              │
│              │            [element]             │              │
│              │               │                  │              │
│              ├───────────────┘─────────────────┤              │ ← Rung 2 (continues)
│              │                                  │              │

1.2 Layout Dimensions

参数默认值含义
power_rail_width4px电源轨线宽
rung_height70px每条梯级高度
rung_spacing15px梯级间隔
element_width32px标准元件宽度
element_height24px标准元件高度（接点/线圈）
rung_wire_y_offsetrung_height / 2梯级横线中心
element_spacing12px相邻元件间隔
left_rail_x20px左侧电源轨 x 坐标
right_rail_xcanvas_width - 20右侧电源轨 x 坐标
label_offset14px标签到元件中心的纵向距离

2. Element Symbols

2.1 Contacts (Inputs — 读取条件)

接点位于梯级左侧区域，表示输入条件。

Normally Open Contact (XIC / NO)

  • 符号: 两条平行竖线，间距 8px，无连接
  • 含义: 当关联 bit = 1 时，接点闭合（导通）
  • SVG: 
    <!-- Left blade -->
<line x1="0" y1="-12" x2="0" y2="12" stroke="#333" stroke-width="2"/>
<!-- Right blade -->
<line x1="8" y1="-12" x2="8" y2="12" stroke="#333" stroke-width="2"/>
<!-- Lead wires (connecting to rung line) -->
<line x1="-12" y1="0" x2="0" y2="0" stroke="#333" stroke-width="2"/>
<line x1="8" y1="0" x2="20" y2="0" stroke="#333" stroke-width="2"/>
<!-- Total width: 32px (−12 to 20) -->

Normally Closed Contact (XIO / NC)

  • 符号: 两条平行竖线 + 斜线穿过（diagonal slash）
  • SVG: 同 NO + 额外斜线: 
    <!-- Diagonal slash across gap -->
<line x1="0" y1="6" x2="8" y2="-6" stroke="#333" stroke-width="2"/>

Positive Transition Contact (ONS / 上升沿)

  • 符号: 两竖线 + 上升边箭头（↑）
  • SVG: NO + <polygon points="4,-6 4,0 8,-3"/> inside gap

Negative Transition Contact (ONF / 下降沿)

  • 符号: 两竖线 + 下降边箭头（↓）
  • SVG: NO + <polygon points="4,6 4,0 8,3"/> inside gap

Comparison Contact (EQU, GRT, LES, etc.)

  • 符号: 矩形盒（24×18px）内含比较符（=, >, <, ≥, ≤, ≠） 
    <rect x="0" y="-9" width="24" height="18" fill="white" stroke="#333" stroke-width="1.5"/>
<text x="12" y="5" font-size="11" text-anchor="middle">≥</text>
<!-- Input/output label references outside the box -->

2.2 Coils (Outputs — 设置输出)

线圈位于梯级右侧（紧靠右侧电源轨），表示输出驱动。

Output Coil (OTE / Standard)

  • 符号: 圆括号 ( ) — 两个相对圆弧
  • SVG: 
    <!-- Left arc -->
<path d="M 0,0 A 8,12 0 0 0 0,0" fill="none"/>
<!-- Cleaner: two arcs forming parentheses shape -->
<path d="M 8,-12 Q 0,-12 0,0 Q 0,12 8,12" fill="none" stroke="#333" stroke-width="2"/>
<path d="M 16,-12 Q 24,-12 24,0 Q 24,12 16,12" fill="none" stroke="#333" stroke-width="2"/>
<!-- Lead wires -->
<line x1="-12" y1="0" x2="8" y2="0" stroke="#333" stroke-width="2"/>
<line x1="16" y1="0" x2="28" y2="0" stroke="#333" stroke-width="2"/>
<!-- Total width: 40px -->

Negated Output Coil (OTN)

  • 同 OTE，内部加 / 斜线或 NOT 标注
  • SVG: <line x1="8" y1="8" x2="16" y2="-8" stroke="#333" stroke-width="1.5"/>

Set Coil / Latch (OTL)

  • 同 OTE，内部加 S 文字
  • SVG: <text x="12" y="5" font-size="12" font-weight="bold" text-anchor="middle">S</text>

Reset / Unlatch Coil (OTU)

  • 同 OTE，内部加 R 文字
  • SVG: 同上，文字 R

Transition Coils (ONS/ONR)

  • 上升沿/下降沿触发，内部加箭头标记

2.3 Function Blocks (复杂功能块)

function block 在梯级中间，矩形盒包含输入/输出 pins。

标准尺寸: 60px wide × 50px tall（最小），根据 pin 数量扩展。

<!-- Function block box -->
<rect x="0" y="0" width="60" height="50"
      fill="white" stroke="#333" stroke-width="2"
      class="lt-function-block"/>
<!-- Block type label (top center) -->
<text x="30" y="14" font-size="11" font-weight="bold"
      text-anchor="middle" class="lt-fb-type">TON</text>
<!-- Divider line under type label -->
<line x1="0" y1="18" x2="60" y2="18" stroke="#333" stroke-width="1"/>
<!-- Input pin labels (left side) -->
<text x="4" y="28" font-size="9">IN</text>
<text x="4" y="40" font-size="9">PT</text>
<!-- Input pin wires (left edge) -->
<line x1="-10" y1="25" x2="0" y2="25" stroke="#333" stroke-width="1.5"/>
<line x1="-10" y1="37" x2="0" y2="37" stroke="#333" stroke-width="1.5"/>
<!-- Output pin labels (right side) -->
<text x="36" y="28" font-size="9">Q</text>
<text x="36" y="40" font-size="9">ET</text>
<!-- Output pin wires (right edge) -->
<line x1="60" y1="25" x2="70" y2="25" stroke="#333" stroke-width="1.5"/>
<line x1="60" y1="37" x2="70" y2="37" stroke="#333" stroke-width="1.5"/>

Timer Blocks

Block类型Pins (Input)Pins (Output)
TONTimer On-DelayIN, PT (preset time)Q (done), ET (elapsed)
TOFFTimer Off-DelayIN, PTQ, ET
TPTimer PulseIN, PTQ, ET
RTORetentive Timer OnIN, PT, R (reset)Q, ET

Counter Blocks

Block类型Pins (Input)Pins (Output)
CTUCount UpCU (count up), R (reset), PV (preset)Q (done), CV (current)
CTDCount DownCD, LD (load), PVQ, CV
CTUDUp/DownCU, CD, R, LD, PVQU, QD, CV

Math Blocks

矩形盒，width=60, height=40，内部: ADD, SUB, MUL, DIV。 Pins: IN1, IN2 (inputs), OUT (output), EN (enable), ENO (enable output).

Comparison Blocks

内部标注: EQU, NEQ, GRT, GEQ, LES, LEQ。 Pins: IN1, IN2, OUT (boolean result).

3. Variable Labels & Addressing

3.1 Label Positioning

每个 contact/coil 上方或下方显示变量地址/tag name：

<!-- Tag name above element -->
<text x="x_center" y="y_rung - element_height/2 - 4"
      font-size="9" font-family="monospace" text-anchor="middle"
      class="lt-tag-label">StartBtn</text>
<!-- Address below element (optional) -->
<text x="x_center" y="y_rung + element_height/2 + 12"
      font-size="8" text-anchor="middle" class="lt-address-label">I:0/0</text>

3.2 Rung Numbers

左侧电源轨外侧显示梯级编号：

<text x="left_rail_x - 8" y="y_rung" font-size="10"
      text-anchor="end" class="lt-rung-number">0001</text>

3.3 Rung Comments

梯级上方可选注释行：

<text x="left_rail_x + 10" y="y_rung - rung_height/2 + 8"
      font-size="10" font-style="italic" fill="#555"
      class="lt-rung-comment">Motor start/stop latch logic</text>

4. Parallel Branches

梯级中的并联分支表示 OR 逻辑：

4.1 Branch Start/End Notation

<!-- Branch Start: vertical line down from rung wire -->
<line x1="x_branch_start" y1="y_rung" x2="x_branch_start" y2="y_branch"
      stroke="#333" stroke-width="2"/>

<!-- Branch parallel wire -->
<line x1="x_branch_start" y1="y_branch" x2="x_branch_end" y2="y_branch"
      stroke="#333" stroke-width="2"/>

<!-- Elements on branch wire (at y_branch level) -->

<!-- Branch End: vertical line back up to rung wire -->
<line x1="x_branch_end" y1="y_branch" x2="x_branch_end" y2="y_rung"
      stroke="#333" stroke-width="2"/>

4.2 Multiple Parallel Branches

每个额外 branch 在 y_branch + branch_spacing 处，默认 branch_spacing = rung_height + 10.

5. DSL Grammar (Ladder Logic)

document       = header statement*
header         = "ladder" quoted_string? NEWLINE

statement      = comment | variable_decl | rung_def

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

variable_decl  = "var" id ":" data_type ("=" init_value)? NEWLINE
data_type      = "bool" | "int" | "float" | "timer" | "counter" | "string"
init_value     = "true" | "false" | INT | FLOAT | quoted_string

rung_def       = "rung" INT? rung_comment? ":" NEWLINE INDENT
                   rung_element+
                 DEDENT

rung_comment   = quoted_string

rung_element   = series_element
               | parallel_block

series_element = contact | coil | function_block | jump

parallel_block = "parallel:" NEWLINE INDENT
                   (series_element+)
                   ("branch:" NEWLINE INDENT series_element+ DEDENT)+
                 DEDENT

contact        = contact_type "(" IDENTIFIER ")" NEWLINE
contact_type   = "XIC" | "XIO" | "ONS" | "ONF"    # NO, NC, rising, falling edge
               | "EQU" | "NEQ" | "GRT" | "GEQ" | "LES" | "LEQ"  # compare

coil           = coil_type "(" IDENTIFIER ")" NEWLINE
coil_type      = "OTE" | "OTN" | "OTL" | "OTU"   # output, negated, set, reset

function_block = fb_type "(" fb_params ")" NEWLINE
fb_type        = "TON" | "TOFF" | "TP" | "RTO"
               | "CTU" | "CTD" | "CTUD"
               | "ADD" | "SUB" | "MUL" | "DIV" | "MOV"
fb_params      = IDENTIFIER ("," IDENTIFIER)*

jump           = "JMP" "(" LABEL_ID ")" NEWLINE
               | "LBL" "(" LABEL_ID ")" NEWLINE

IDENTIFIER     = /[a-zA-Z][a-zA-Z0-9_]*/
LABEL_ID       = /[a-zA-Z][a-zA-Z0-9_]*/
INT            = /[0-9]+/
FLOAT          = /[0-9]+\.[0-9]+/
quoted_string  = '"' /[^"]*/ '"'
INDENT         = increase in whitespace
DEDENT         = decrease in whitespace
NEWLINE        = /\n/

DSL 示例（Motor Start/Stop）：

ladder "Motor Control"

var StartBtn: bool
var StopBtn: bool
var EmergencyStop: bool = false
var MotorLatch: bool = false
var MotorRun: bool = false
var RunIndicator: bool = false

rung 0 "Start latch with stop condition":
  XIC(StartBtn)
  XIO(StopBtn)
  XIO(EmergencyStop)
  OTL(MotorLatch)

rung 1 "Unlatch on E-stop":
  XIC(EmergencyStop)
  OTU(MotorLatch)

rung 2 "Motor run output":
  XIC(MotorLatch)
  OTE(MotorRun)

rung 3 "Run indicator":
  XIC(MotorRun)
  OTE(RunIndicator)

DSL 示例（Timer + Counter）：

ladder "Timer Counter Example"

var RunSignal: bool
var RunTimer: timer
var CycleCounter: counter
var AlarmOut: bool

rung 0 "TON timer when running":
  XIC(RunSignal)
  TON(RunTimer, RunSignal, T#5s)

rung 1 "Count on timer done":
  XIC(RunTimer.Q)
  CTU(CycleCounter, RunTimer.Q, 100)

rung 2 "Alarm when max cycles":
  XIC(CycleCounter.Q)
  OTE(AlarmOut)

DSL 示例（Parallel Branch — OR logic）：

ladder "Parallel Branch"

rung 0 "Start from push button OR remote":
  parallel:
    XIC(LocalStart)
    branch:
      XIC(RemoteStart)
  XIC(MotorLatch)
  XIO(StopBtn)
  OTE(MotorRun)

6. SVG Structure

<svg class="lt-ladder" data-diagram-type="ladder">
  <defs>
    <style>
      .lt-power-rail   { stroke: #333; stroke-width: 4; fill: none; }
      .lt-rung-wire    { stroke: #333; stroke-width: 2; fill: none; }
      .lt-contact      { stroke: #333; stroke-width: 2; fill: none; }
      .lt-coil         { stroke: #333; stroke-width: 2; fill: none; }
      .lt-fb-box       { stroke: #333; stroke-width: 2; fill: white; }
      .lt-fb-type      { font: bold 11px monospace; fill: #333; }
      .lt-tag-label    { font: 9px monospace; fill: #333; }
      .lt-address      { font: 8px monospace; fill: #666; }
      .lt-rung-number  { font: 10px monospace; fill: #999; }
      .lt-rung-comment { font: italic 10px sans-serif; fill: #555; }
      .lt-branch-wire  { stroke: #333; stroke-width: 2; fill: none; }
    </style>
  </defs>
  <title>Ladder Logic Diagram — [name]</title>
  <desc>[description]</desc>

  <!-- Left power rail -->
  <line class="lt-power-rail" x1="20" y1="0" x2="20" y2="{total_h}"/>

  <!-- Right power rail -->
  <line class="lt-power-rail" x1="{w-20}" y1="0" x2="{w-20}" y2="{total_h}"/>

  <!-- Rungs -->
  <g id="lt-rungs">
    <g id="rung-0" data-rung="0">
      <!-- Rung number -->
      <text class="lt-rung-number" ...>0000</text>
      <!-- Rung comment -->
      <text class="lt-rung-comment" ...>Motor start/stop</text>
      <!-- Rung horizontal wire -->
      <line class="lt-rung-wire" x1="20" y1="y" x2="{w-20}" y2="y"/>
      <!-- Elements in rung -->
      <g id="rung-0-elem-0" data-type="XIC" data-tag="StartBtn">
        <!-- contact SVG -->
        <text class="lt-tag-label" ...>StartBtn</text>
      </g>
      <g id="rung-0-elem-1" data-type="OTL" data-tag="MotorLatch">
        <!-- coil SVG -->
        <text class="lt-tag-label" ...>MotorLatch</text>
      </g>
    </g>
  </g>
</svg>

7. Test Cases

Case 1: Single Contact → Single Coil

ladder
rung 0:
  XIC(MotorStart)
  OTE(MotorOut)

验证：一条梯级，左侧 NO contact，右侧 output coil，两端连接电源轨。

Case 2: Series Contacts (AND logic)

ladder
rung 0:
  XIC(A)
  XIC(B)
  XIO(C)
  OTE(Y)

验证：A/B/C 三个接点串联，C 为 NC（有斜线）。

Case 3: Parallel Branch (OR logic)

ladder
rung 0:
  parallel:
    XIC(Btn1)
    branch:
      XIC(Btn2)
  OTE(Lamp)

验证：Btn1 和 Btn2 并联分支，结尾合并后接 Lamp 线圈。

Case 4: TON Timer

ladder
var RunTimer: timer
rung 0:
  XIC(StartSignal)
  TON(RunTimer, StartSignal, T#10s)
rung 1:
  XIC(RunTimer.Q)
  OTE(DoneOutput)

验证：TON block 显示 IN 和 PT 输入 pins，Q 输出 pin，T#10s 参数标注。

Case 5: Set/Reset Latch

ladder
rung 0:
  XIC(SetBtn)
  OTL(MotorLatch)
rung 1:
  XIC(ResetBtn)
  OTU(MotorLatch)

验证：OTL 线圈内显示 S，OTU 线圈内显示 R。

Case 6: Counter

ladder
var PulseCnt: counter
rung 0:
  XIC(PulseInput)
  CTU(PulseCnt, PulseInput, 50)
rung 1:
  XIC(PulseCnt.Q)
  OTE(BatchDone)

验证：CTU block 有 CU/PV inputs，Q output，梯级 1 读取 .Q 位。

8. Implementation Priority

PriorityFeatureComplexity用户价值
P0 (MVP)XIC, XIO contacts + OTE coilLowCore — 90% 梯级用这三个
P0Power rails + rung horizontal wireLowCore
P0Series elements layoutLowCore
P0Tag name labels above elementsLowCore
P1OTL (Set) / OTU (Reset) coilsLowHigh
P1Parallel branch (OR logic)MediumHigh — 工业逻辑必须
P1TON / TOFF timer blocksMediumHigh
P1CTU counter blockMediumHigh
P1ONS / ONF transition contactsLowMedium
P2Comparison contacts (EQU, GRT, etc.)MediumMedium
P2Math blocks (ADD, SUB, MOV)MediumMedium
P2Rung comments + rung numbersLowMedium
P2CTUD up/down counterMediumLow
P3JMP / LBL jump instructionsMediumLow
P3IEC symbol style (vs NEMA)MediumLow

Circuit schematic

Analog and digital circuit schematics from SPICE-style netlist or positional DSL. Auto-routed power/ground rails, orthogonal signal wiring, IEEE standard component symbols.

Single-line diagram (SLD)

Power system one-line diagrams following IEEE 315. Substation and distribution layouts with transformers, breakers, disconnects, buses, and protective relays. For electrical engineering, utilities, and power distribution.

On this page

1. Structure & Layout1.1 Overall Diagram Structure1.2 Layout Dimensions2. Element Symbols2.1 Contacts (Inputs — 读取条件)Normally Open Contact (XIC / NO)Normally Closed Contact (XIO / NC)Positive Transition Contact (ONS / 上升沿)Negative Transition Contact (ONF / 下降沿)Comparison Contact (EQU, GRT, LES, etc.)2.2 Coils (Outputs — 设置输出)Output Coil (OTE / Standard)Negated Output Coil (OTN)Set Coil / Latch (OTL)Reset / Unlatch Coil (OTU)Transition Coils (ONS/ONR)2.3 Function Blocks (复杂功能块)Timer BlocksCounter BlocksMath BlocksComparison Blocks3. Variable Labels & Addressing3.1 Label Positioning3.2 Rung Numbers3.3 Rung Comments4. Parallel Branches4.1 Branch Start/End Notation4.2 Multiple Parallel Branches5. DSL Grammar (Ladder Logic)6. SVG Structure7. Test CasesCase 1: Single Contact → Single CoilCase 2: Series Contacts (AND logic)Case 3: Parallel Branch (OR logic)Case 4: TON TimerCase 5: Set/Reset LatchCase 6: Counter8. Implementation Priority