LADDER LOGICResources / Ladder logic symbolsUpdated 29 Oct 2026

Ladder logic coil symbols: output, negated, set and reset

Coils are the result of a rung. A coil writes a bit: an output to the field, or an internal flag that other rungs read with contacts.

SymbolIEC 61131-3What it is

Output coilWrites the result of the rung to a bit: 1 while the rung is true, 0 when it is false.

Negated coilWrites the opposite of the rung: 0 while the rung is true, 1 when it is false.

Set (latch) coilSets its bit to 1 when the rung is true and leaves it at 1 when the rung goes false.

Reset (unlatch) coilResets its bit to 0 when the rung is true.

Coils

An output coil (OTE) follows the rung: on while the rung is true, off when it is false. Set and reset coils (OTL and OTU, latch and unlatch) only act when the rung is true and otherwise leave the bit as it is, so a set bit stays on until a reset coil clears it.

Use each output coil once in a program. Writing the same bit from two rungs means the last one scanned wins, a common cause of outputs that flicker or ignore a rung.

Frequently asked questions

Which coils appear on a ladder diagram?

This legend covers output coil, negated coil, set (latch) coil, reset (unlatch) coil. Project legends may add more.

Can I download these symbols?

Yes. Each symbol page has free SVG files, and the hub has printable PDF charts.

Every interlock in your PLC logic, tested and signed.Deskely holds the cause and effect and function test records for every system, checked as they are signed, so the logic is proved before start-up.

In production since 2014
Thousands of daily users
On MODEC FPSO projects since 2016

See Deskely on your project How Verify works

Other categories5 symbolsLadder logic contact symbols: NO, NC and edge contacts 3 symbolsLadder rung, series and parallel branch symbols 5 symbolsPLC timer and counter symbols: TON, TOF, TP, CTU, CTD 12 symbolsLadder compare, move, math, edge and latch blocks

Coils

Frequently asked questions

Autonomous engineering runs on Deskely.