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Newbie u931803
Newbie
6,066 Views
Registered: ‎08-04-2011

Virtex6 change IO driving at run-time

hi,

 

is there any way i can change the IO driving at run-time?

 

thanks

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7 Replies
Teacher eteam00
Teacher
6,061 Views
Registered: ‎07-21-2009

Re: Virtex6 change IO driving at run-time

You mean change output from '0' to '1' or 'z' ?  YES!

 

You mean change output current from '8mA' to '32ma'?   Nope, this is a setting fixed in the configuration.

You mean change output 'IOSTANDARD' from 'LVCMOS' to 'SSTL' ?  Nope, this is a setting fixed in the configuration.

 

-- Bob Elkind

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Xilinx Employee
Xilinx Employee
6,057 Views
Registered: ‎01-03-2008

Re: Virtex6 change IO driving at run-time

> You mean change output current from '8mA' to '32ma'?   Nope, this is a setting fixed in the configuration.

> You mean change output 'IOSTANDARD' from 'LVCMOS' to 'SSTL' ?  Nope, this is a setting fixed in the configuration.

 

 It is possible to partially reconfigure the I/O to change to the configuration bits to something else, but this would be for an advanced user and may introduce glitches during the reconfiguration.   It would be a very unusual system that would requiring changing these dynamically.

 

 

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Teacher eteam00
Teacher
6,055 Views
Registered: ‎07-21-2009

Re: Virtex6 change IO driving at run-time

> You mean change output current from '8mA' to '32ma'?   Nope, this is a setting fixed in the configuration.

> You mean change output 'IOSTANDARD' from 'LVCMOS' to 'SSTL' ?  Nope, this is a setting fixed in the configuration.

 

It is possible to partially reconfigure the I/O to change to the configuration bits to something else, but this would be for an advanced user and may introduce glitches during the reconfiguration.   It would be a very unusual system that would requiring changing these dynamically

 

Excellent point.  And this can be taken one step further...

 

Full (rather than partial) reconfiguration can also be used to change... just about anything in the design, including IO signal standards and drive levels.

 

Full reconfiguration can be much simpler to implement than partial reconfiguration. For example, if the FPGA is configured in slave mode by an onboard processor, it's a simple matter for the processor to re-configure the FPGA with an alternate 'program' or configuration file/bitstream.

 

-- Bob Elkind

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Summary:
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Teacher eteam00
Teacher
6,054 Views
Registered: ‎07-21-2009

Re: Virtex6 change IO driving at run-time

Yet another approach to this question:

 

If you want to switch between two different IOSTANDARDs, there are SOME standards which can be switched in normal 'run-time' operation.  Here are some examples.

 

Switch drive current

Implement two outputs, connected externally on the circuit board.  One output is 2mA drive, the other is 32mA drive (for example).  Enable one or the other output (using output enable) to switch output drive level.

 

Switch between two IOSTANDARDs for output drive

Implement two outputs, connected externally on the circuit board.  One output is LVTTL33, the other is LVCMOS25 (for example).  Enable one or the other output (using output enable) to switch output standard.

 

Switch between push-pull and open-drain output

Use the output enable facility to (under logic control) de-assert output enable when the output signal is '1', and assert output enable when the output signal is '0'.

 

I'm sure there are other interesting combinations.  In all cases, be mindful of datasheet min and max input and output voltage levels, which are sometimes a function of VCCO or VCCAUX volatges.  Also be mindful of possible high-current situations which should be avoided (can't give you an example, but I can't prove the problem doesn't exist).

 

-- 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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Historian
Historian
6,049 Views
Registered: ‎02-25-2008

Re: Virtex6 change IO driving at run-time


@mcgett wrote:

> You mean change output current from '8mA' to '32ma'?   Nope, this is a setting fixed in the configuration.

> You mean change output 'IOSTANDARD' from 'LVCMOS' to 'SSTL' ?  Nope, this is a setting fixed in the configuration.

 

 It is possible to partially reconfigure the I/O to change to the configuration bits to something else, but this would be for an advanced user and may introduce glitches during the reconfiguration.   It would be a very unusual system that would requiring changing these dynamically.

 

 



I wonder if the OP is reading Micron's Technical Note TN-46-08: Initialization Sequence for DDR SDRAM. Because this document says, on page 1, Step 3, "Assert and hold clock enable (CKE) to an LVCMOS logic LOW level. During the initial power ramp, the CKE input will not recognize SSTL_2 logic levels."

 

V4 data sheet says that Vol for LVCMOS25 is 0.4V max, and Vol for SSTL2 Class 1 is VTT-0.61 max. So with VTT set to 1.25 V, Vol is 0.64 V. Furthermore, a footnote in the Micron DDR data sheet says regarding validity of inputs before VREF stabilizes, "Exception: during the period before VREF stabilizes, CKE < 0.3 × VDD is recognized as LOW." So 2.5 V * 0.3 = 0.75, so I think the Micron tech note doth worry too much.

----------------------------Yes, I do this for a living.
Teacher eteam00
Teacher
6,046 Views
Registered: ‎07-21-2009

Re: Virtex6 change IO driving at run-time

I wonder if the OP is reading Micron's Technical Note TN-46-08: Initialization Sequence for DDR SDRAM....

 

Wow!  Bassman, that inference would never have ocurred to me in a zillion years.

 

I had to give your post a kudo -- for either genius or astonishing imagination, whichever it may turn out to be.

 

-- 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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Historian
Historian
6,024 Views
Registered: ‎02-25-2008

Re: Virtex6 change IO driving at run-time


@eteam00 wrote:

I wonder if the OP is reading Micron's Technical Note TN-46-08: Initialization Sequence for DDR SDRAM....

 

Wow!  Bassman, that inference would never have ocurred to me in a zillion years.

 

I had to give your post a kudo -- for either genius or astonishing imagination, whichever it may turn out to be.

 

-- Bob Elkind


It was neither genius nor imagination ... I wrote a DDR SDRAM controller not too long ago, and that particular bit about "must use LVCMOS levels at startup" struck me as particularly ... weird.

----------------------------Yes, I do this for a living.
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