Intel® Arria® 10 Core Fabric and General Purpose I/Os Handbook

ID 683461
Date 1/21/2022
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5.5.3.4. Programmable Open-Drain Output

The programmable open-drain output provides a high-impedance state on output when logic to the output buffer is high. If logic to the output buffer is low, output is low.

You can attach several open-drain outputs 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.

You can enable the open-drain output assignment using one of these methods:
  • Design the tristate buffer using OPNDRN primitive.
  • Turn on the Auto Open-Drain Pins option in the Intel® Quartus® Prime software.
You can design open-drain output without enabling the option assignment. However, your design will not use the I/O buffer's open-drain output feature. The open-drain output feature of the I/O buffer provides you the best propagation delay from OE to output.