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.
IEC
IEC · 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.
In plain English
What does IEC open-circuit output, L-type (open collector) mean?
The underlined diamond marks an output, such as an NPN open collector or an N-channel open drain, that can supply a relatively low-impedance L level when on and is open when off. An external pull-up is needed. TI's public overview notes this output type supports a positive-logic wired-AND connection.
A simple example
When a variant with a built-in passive pull-up exists, a further mark inside the diamond distinguishes it. Reviewing the exact additional drawing mark tells the drafter whether an external pull-up must be added to the schematic.
What the drawings help you do
The additional drawing mark does not state the maximum pull-up voltage. Some open-drain outputs tolerate a higher pull-up rail than the device supply and some do not.
This particular reference
Underlined diamond inside an outline: an open-circuit output that can only drive a low level. The H-type open-circuit output has the line above the diamond and drives a high level only.
- Terminal
- An identified point where a conductor connects.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
- Rating
- A value stating the conditions for which equipment is specified.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · Diamond with underline 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-L
What it represents
The underlined diamond marks an output, such as an NPN open collector or an N-channel open drain, that can supply a relatively low-impedance L level when on and is open when off. An external pull-up is needed. TI's public overview notes this output type supports a positive-logic wired-AND connection.
When a variant with a built-in passive pull-up exists, a further mark inside the diamond distinguishes it. Reviewing the exact qualifier tells the drafter whether an external pull-up must be added to the schematic.
The qualifier does not state the maximum pull-up voltage. Some open-drain outputs tolerate a higher pull-up rail than the device supply and some do not.
How to read it
- Underline below the diamond: pulls low only.
- Find the external pull-up on the net.
Information to show or reference
- Draw the diamond with its underline next to the output.
- Show the pull-up resistor.
- Record the permitted pull-up voltage.
A distinction that matters
The H-type open-circuit output has the line above the diamond and drives a high level 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 L-type open-circuit output qualifier and wired-AND 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.
Explore related references
Put the reference into a drawing workflow.
Elora Grid helps electrical teams work with drawings, specifications and equipment information. Explore the drafting workflow or join the early-access waitlist.