OC-L
IEC open-circuit output, L-type (open collector)
Underlined diamond inside an outline: an open-circuit output that can only drive a low level.
IEC
IEC · OC-H
IEC open-circuit output, H-type (open emitter)
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.
- 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.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · 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.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · OC-H
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.
A distinction that matters
The L-type output has its line under the diamond and drives low only.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
Describes the H-type open-circuit output and wired-OR capability.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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