Answers Database

XC3000/XC4000/XC5200: Can device I/Os be configured as an open-drain (open-collector)?


Record #1651

Problem Title:
XC3000/XC4000/XC5200: Can device I/Os be configured as an open-drain
(open-collector)?



Problem Description:
Keywords: OBUFT, open collector,drain, IO, output, input.

Urgency: Standard

Description

It is often useful to have open-drain or open-collector
outputs so that multiple outputs may be connected to a
single input, such as a reset line.
Can I configure my Xilinx device to have open-drain
outputs?


Solution 1:

With most all Xilinx devices, an open-drain type output may be
configured.  Schematically, this type of output should look
like the following :


Output Signal ----------|
			|
		      |\|	   ______
	      ________| \_________/ OPAD |
	      |       | /	  \______|
	    __|__     |/
	     ___     OBUFT
	      _
	     GND

This sort of circuitry may also be described in HDL code.



End of Record #1651