AR# 1651

描述

It is often useful for a device to contain open-drain or open-collector outputs so that multiple outputs can be connected to a single input, such as a reset line.

Can I configure my Xilinx device to include open-drain outputs?

How do I configure my Xilinx device I/O as an open-drain (open-collector)?

解决方案

With all Xilinx devices, an open-drain type output is not available directly but canbe configured. Schematically, this type of output should look like the following:

Open-Drain Output

This type of circuitry can also be described in HDL code.

Infer the open drain buffer by using the following code:

VHDL:

dout <= 'Z' when din='1' else '0';

Verilog:

always @(ENABLE)
if (ENABLE)
DOUT = 1'bZ;
else
DOUT = 1'b0;