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楼主 |
发表于 2010-3-14 12:48:29
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1.对于问题2中的weak-keeper,我先找了官方网站上的一些资料:
Description
Keywords: Spartan-3, weak, keeper, I/O, IO, terminate, termination, bus, hold, DCI, XCITE, pullup, pull-up, pulldown, pull-down, resistor
The keeper circuitry is designed to hold a bus at a known value in the event that all drivers on that bus are disabled. The circuitry essentially consists of a pull-up or pull-down resistor. Will this feature work in the presence of DCI termination?
Solution
The keeper circuitry works on all I/Os (DCI or non-DCI) that are series terminated, such as LVTTL and LVCMOS. However, any parallel termination resistors (e.g., those used with SSTL or HSTL standards) prevent the keeper from performing its function because it is not as strong as the 50 Ohm pull-ups/downs.
In addition, since the keeper upsets the balance of such terminations, it is not activated for the DCI standards employing parallel termination (although the software might indicate this by accepting the KEEPER attribute without issuing an error message).
这是有人在官方网站上回答的问题。
我来翻译一下:
问题:
这个保持电路是为了当没有驱动的时候,使总线保持可知的电平。这个总线本质上是由一个上拉和一个下拉电阻组成的。那么这个功能在“计算机显示接口”还能用吗?
答案:
这个保持电路在所有的串行I/O上都有用,比如LVTTL电平和LVCMOS电平。但是在所有的并联的电阻(比如SSTL和HSTL中)都会阻止这个功能,因为他的驱动能力没有50欧姆的上下拉的能力强。
另外,由于这个保持电路会影响终端的稳定,所以在DCI上的标准时不被使用的(当然你使用了软件也不会报错)。 |
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