AR# 51834

描述

The Design Assistant will walk you through the recommended design flow for SelectIO while debugging commonly encountered issues. 

The Design Assistant will not only provide useful design and troubleshoot information but also point you to the exact documentation you need to read to help you design efficiently with SelectIO.

Note: This article is part of Xilinx SelectIO Solution Center (Xilinx Answer 50924). 

The Xilinx SelectIO Solution Center is available to address all questions related to SelectIO whether you are starting a new design or troubleshooting a problem, use the SelectIO Solution Center to guide you to the right information.

This Answer record addresses frequently asked questions about the effect on reliability from driving (or over driving) the I/Os.

解决方案

1) What is the maximum voltage an I/O can be driven to?

The answer is broken into two cases. 

Firstly the steady state is addressed by the device data sheet specification called Vin and this should not be exceeded.

Secondly if the max and min values are of short duration (in relation to the bit period) this is called Overshoot and Undershoot.

Some of data sheet contain the specifications for the amount and duration of allowable over and under shoot.

For 7 Series devices, there are a set of AC overshoot numbers in the data sheet.

(Xilinx Answer 61125) serves as a good guide to interpreting these numbers.

(Xilinx Answer 10835) addresses the question of whether I/Os can be driven to 5V. 

For information on Spartan-3/3E see (Xilinx Answer 19547).

2) Where to find information on ESD?

A good first port of call is (Xilinx Answer 3982)

Xilinx recommends not to leave any pins (including unused pins) floating. Leaving pins floating reduces their ESD protection. For more information, see (Xilinx Answer 11906).

(Xilinx Answer 9048) lists the pins that have clamp diodes.

(Xilinx Answer 3982) contains links to the Reliability Report which contains the results of Xilinx testing for ESD.

3) Which devices are Hot Swappable?

7 Series is addressed in (Xilinx Answer 44225).

(Xilinx Answer 37347) provides additional details on driving unpowered 7 Series I/O.

(Xilinx Answer 45985) outlines some techniques for dealing with the situation where you drive an unpowered pin and back-power the rail.

6 Series is addressed in (Xilinx Answer 40416).

4) What state are the I/Os in at power up?

The device data sheet contains a recommended power sequence, in order to guarantee the state of the I/Os at power on the recommendation must be followed. 

If the recommendation is followed the I/Os will be either 3-stated or pulled up depending on the HSWAP_EN or PUDC_B.

See (Xilinx Answer 50802) for further information on 7 Series behavior.

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