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Visitor jobsb
Visitor
11,639 Views
Registered: ‎01-28-2011

HSWAPEN pin as user IO

Hi,

 

I have a board with Spartan-6 mounted on it.

I am using HSWAP pin as an User I/O.

I forgot to put an external pull-down resitor on HSAWP pin, will it have any problem in configuring the FPGA ?

please help me.

 

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13 Replies
Scholar austin
Scholar
11,637 Views
Registered: ‎02-27-2008

Re: HSWAPEN pin as user IO

j,

 

Page 38:

 

http://www.xilinx.com/support/documentation/user_guides/ug380.pdf

 

Tells you what the pin does.  So, I ask you the question, does it matter to how you have wired your board if the IOs are pulled high with weak pullups, or if they are floating while the device configures?

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor jobsb
Visitor
11,628 Views
Registered: ‎01-28-2011

Re: HSWAPEN pin as user IO

 
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Visitor jobsb
Visitor
11,625 Views
Registered: ‎01-28-2011

Re: HSWAPEN pin as user IO

Austin,

 

the hswapen is used as an IO for wiring the pci bus.

 

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Scholar austin
Scholar
11,615 Views
Registered: ‎02-27-2008

Re: HSWAPEN pin as user IO

j,

 

So, if the pin is floating while the part is configured, how does that matter?


If the pin is floating, it might be high, in which case all the other IO will be pulled high weakly, or it might be low, in which case all the other IO will be left floating.


Consider both cases for all other IO, and for this pin,m consider it is floating:  neither high, nor low.


How will that affect the application?  Once the part is configured, everything will be as you have programmed it to be, so this is only what happens, before DONE goes high.

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor jobsb
Visitor
11,594 Views
Registered: ‎01-28-2011

Re: HSWAPEN pin as user IO

Austin,

 

In simple words, that means the fpga will be configured without any issues.

am i right?

 

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Instructor
Instructor
11,587 Views
Registered: ‎07-21-2009

Re: HSWAPEN pin as user IO

Austin, In simple words, that means the fpga will be configured without any issues. am i right?

I hope Austin will forgive me for this kibitz...

 

J,  What Austin is saying is

 

  • the input level of the HSWAPEN pin will not, by itself, prevent successful FPGA configuration.
  • the indeterminate state of the HSWAPEN pin may affect other circuitry on the board, and this may interfere with successful configuration.  As the board designer, it is up to you to chase down these possibilities and rule them out as potential problems, one by one.

If your FPGA configures unreliably, that might be the result of indirect interference which might be attributable to the HSWAPEN pin use.  This assertion involves at least three "might" and "if" conditions.

 

- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Scholar austin
Scholar
11,533 Views
Registered: ‎02-27-2008

Re: HSWAPEN pin as user IO

Bob,


Your help is greatly appreciated.  Anytime.

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor jobsb
Visitor
11,517 Views
Registered: ‎01-28-2011

Re: HSWAPEN pin as user IO

Austin, Bob,

 

Thanks.

On Page 39 of Ug380.pdf, the HSWAPEN pin is INPUT before configuration and is an IO only after configuration.

Does this really matter?

What if it is used as an output?

 

 

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Scholar austin
Scholar
11,513 Views
Registered: ‎02-27-2008

Re: HSWAPEN pin as user IO

j,

 

If you want to use it as an output, be sure to pull it high, or low, with a large enough resistor, so that when it becomes an output, you are not driving a low resistance to Vcco, or to ground.  Best practice is not to leave it floating, but to assert it (waekly) with a resistor just small enough to guarantee  a low, or a high.

 

The worst case leakage on any IO pin is + or - 10uA.  So, for example, I would like to supply 10 uA with less than a .1v voltage drop, I get .1/20uA, or about 10 Kohms.   Now 10 Kohms is a very small load for even the weakest output driver (2mA), so it can be ignored after configuration.

 

 

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Visitor jobsb
Visitor
4,916 Views
Registered: ‎01-28-2011

Re: HSWAPEN pin as user IO

Austin,

 

The pin has been used as an IO (in this case as an output). There is no provision now to pull it high or low through resistor.

 

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Instructor
Instructor
4,902 Views
Registered: ‎07-21-2009

Re: HSWAPEN pin as user IO

The pin has been used as an IO (in this case as an output). There is no provision now to pull it high or low through resistor.

In response to your original post --

I forgot to put an external pull-down resitor on HSAWP pin, will it have any problem in configuring the FPGA ?

The answer is still maybe yes, maybe no, depending on what else is "happening" on the board.

 

Are you seeing any odd or inconsistent behaviour with respect to FPGA configuration?  If yes, then it would be a good idea to dig a bit deeper.

 

- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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Highlighted
Newbie sutejmalaya
Newbie
4,646 Views
Registered: ‎10-25-2011

Re: HSWAPEN pin as user IO

Hello Austin,



I am new to schematic design and i missed a pulldown on HSWAPEN. Now i am using it as an normal IO



Can we keep the PULLDOWN attribute to HSWAPEN during Configuration ??
Tags (1)
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Instructor
Instructor
4,631 Views
Registered: ‎07-21-2009

Re: HSWAPEN pin as user IO

sutejmalaya,

 

1. Please do not attach a new question or topic to an existing thread.  Start a new thread!

 

2. When posting a request for help, please include all the necessary and useful details.  For example, you do not specify which FPGA family you are using!

 

3.  For each FPGA family, Xilinx provides a through and exhaustive Configuration User Guide.  In each of the Configuration User Guides you will find descriptions of the behaviour of all FPGA pins for

 

  • before configuration
  • during configuration
  • after configuration

For the Spartan-6 family, the Configuration User Guide is document UG380.

For Spartan-3/3a/3e/3an families, the Configuration User Guide is document UG332.

 

Can we keep the PULLDOWN attribute to HSWAPEN during Configuration ??

 

4.  The PULLDOWN attribute does not have any effect until after configuration is successfully completed.  You must control the logic level of the HSWAPEN pin before and during configuration, either with external component(s) or with the provided internal weak pullup.

 

If you have additional questions, I recommend you start a new thread.

 

-- Bob Elkind

SIGNATURE:
README for newbies is here: http://forums.xilinx.com/t5/New-Users-Forum/README-first-Help-for-new-users/td-p/219369

Summary:
1. Read the manual or user guide. Have you read the manual? Can you find the manual?
2. Search the forums (and search the web) for similar topics.
3. Do not post the same question on multiple forums.
4. Do not post a new topic or question on someone else's thread, start a new thread!
5. Students: Copying code is not the same as learning to design.
6 "It does not work" is not a question which can be answered. Provide useful details (with webpage, datasheet links, please).
7. You are not charged extra fees for comments in your code.
8. I am not paid for forum posts. If I write a good post, then I have been good for nothing.
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