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Power-User

Join Date: Jan 2007
Location: Berlin (Germany)
Posts: 332
Good Answers: 1

FPGA Output Misbehavior

01/18/2007 8:25 AM

Hello,

we`ve to do some programming of Virtex 4 - PPGA in a security-sensitive application and have the problem that the I/Os get high during configuration. Is it a "must" to disable the outputs during programming in order to have a predictable status under all circumstances with, lets say, a CPLD ??

Thank you for an answer

uweka

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Guru
Engineering Fields - Electrical Engineering - New Member

Join Date: Sep 2006
Location: El Lago, Texas, USA
Posts: 2639
Good Answers: 65
#1

Re: FPGA Output Misbehavior

01/18/2007 10:42 AM

With no program, there is not way to configure the outputs, so they float. The solution is to use a part that is hard programmed, rather than programmed at power-up from a prom. An example would be Actel antifuse based devices. These devices can be programmed off board or on board, but, once programmed, they hold their code. So the I/O are good to go at power-up. Most FPGA manufacturers offer a family with this option.

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Anonymous Poster
#2

Re: FPGA Output Misbehavior

01/18/2007 11:03 PM

That "High" state may be just the effect of a weak pull-up during configuration, say some 100K to 1Mohm, set for every I/O pin.

If you have a HIGH-DURING-CONFIGURATION (HDC) pin programmed to LOW state after configuration, and place a pull down resistor in some of the other I/Os, you may compare exactly what is going on right at the end of configuration, and may be that all of them will stay at LOW state during configuration.

Regrettably I have not used a Virtex 4 yet, but I suspect that this HIGH state of the I/Os during config is not a real HIGH State, just a very weak High State.

Jaime Soto Figueroa

http://www.matharts.cl/

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Associate

Join Date: Nov 2006
Location: Chennai - India
Posts: 29
#3
In reply to #2

Re: FPGA Output Misbehavior

01/19/2007 12:14 AM

I also used micro controller 89c52 and others all are have these same problem, intialy all ports are high in state we also did the same pull down process, its a very easier and cheaper one to make or fix a controller output in a require level , it help only at the power up state after that we can change this value through programaticaly.

Thank you for your valuable suggestions.

K.P.Mahalingam,

Electrical engineer,

India.

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