# IEC open-circuit output, H-type (open emitter)

Canonical URL: https://eloragrid.ai/symbols/iec-open-circuit-output-h-type
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: OC-H
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Diamond with overline inside the outline at the output
Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier.

Overlined diamond at an output: an open-emitter or open-source stage that can only drive a high level.

## In plain English

### What does IEC open-circuit output, H-type (open emitter) mean?

The H-type open-circuit output is drawn as a diamond with a line above it. It can supply a relatively low-impedance H level when on and is open when off, so it needs an external pull-down. TI's public overview notes it supports a positive-logic wired-OR connection.

### A simple example

Open-emitter outputs are typical of emitter-coupled logic and some line drivers. On a drawing the pull-down or termination must be shown, often to a negative or termination rail rather than to ground.

### What the drawings help you do

The additional drawing mark does not give the termination value or rail. Those come from the logic family's application guidance and the device datasheet.

### This particular reference

Overlined diamond at an output: an open-emitter or open-source stage that can only drive a high level. The L-type output has its line under the diamond and drives low only.

### Terms

- Terminal: An identified point where a conductor connects.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf)


## What it represents

The H-type open-circuit output is drawn as a diamond with a line above it. It can supply a relatively low-impedance H level when on and is open when off, so it needs an external pull-down. TI's public overview notes it supports a positive-logic wired-OR connection.
Open-emitter outputs are typical of emitter-coupled logic and some line drivers. On a drawing the pull-down or termination must be shown, often to a negative or termination rail rather than to ground.
The qualifier does not give the termination value or rail. Those come from the logic family's application guidance and the device datasheet.

## How to read it

- Overline above the diamond: drives high only.
- Find the pull-down or termination on the net.

## Information to show or reference

- Draw the diamond with its overline next to the output.
- Show the pull-down or termination and its rail.
- Avoid joining H-type and L-type outputs on one net.

## Important distinction

The L-type output has its line under the diamond and drives low only.

## Facts

- Drives: High level only
- Wired connection: Wired-OR in positive logic
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Describes the H-type open-circuit output and wired-OR capability.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.