5.8.7. Open-Drain Output
The optional open-drain output for each I/O pin is equivalent to an open collector output. If it is configured as an open drain, the logic value of the output is either high-Z or logic low.
You can attach several open-drain output to a wire. This connection type is like a logical OR function and is commonly called an active-low wired-OR circuit. If at least one of the outputs is in logic 0 state (active), the circuit sinks the current and brings the line to low voltage.
You can use open-drain output if you are connecting multiple devices to a bus. For example, you can use the open-drain output for system-level control signals that can be asserted by any device or as an interrupt.
- Design the tristate buffer using OPNDRN primitive.
- Turn on the Auto Open-Drain Pins option in the Intel® Quartus® Prime software.
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