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Observer fatima06
Observer
8,650 Views
Registered: ‎11-03-2011

error : Place : 899

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Hi,

 

I am using a Virtex-5 device in a XC5VLx50T package. Using a DCI output signal in Bank 22 and  LVCMOS25 in the other banks, PAR errors out:

 

ERROR:Place:899 - The following IOBs use the Digitally Controlled Impedance feature (DCI) and have been locked (LOC constraint) to the I/O bank 3. This feature requires the VRN and VRP pins within the same I/O bank to be connected to reference resistors. The following VR pins are currently locked and can't be used to supply the necessary reference.

IO Standard: Name = LVDCI_25, VREF = NR, VCCO = 2.50, TERM = DRIVER

List of locked IOB's: my_dci_output

 

Can you please help me with this problem?

 

Thank you

 

Fatima

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1 Solution

Accepted Solutions
Guide avrumw
Guide
16,432 Views
Registered: ‎01-23-2009

Re: error : Place : 899

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When you use DCI I/O in a bank, the tools have no way of knowing if you have placed the resistors on the appropriate pins. The only check it does is to make sure that there are no user I/O on the VRP and VRN pins. The message you are seeing seems to indicate that the tool thinks that there are user I/Os on at least one of the two VRP/VRN pins.

 

You don't need to and (as far as I know) there is no way to tell the tools that you are planning to connect the reference resistors to the VRP and VRN pins - just make sure the pins are not used for anything else (and, of course, be sure to actually connect the reference resistors on your board).

 

The DCI_VALUE attribute is only for IBIS generation, and should be applied to the IOB using DCI (not the VRP/VRN reference pin). In fact, it is possible that having this attribute on the VRP/VRN pins could confuse the tool into thinking that the pins are not available - you should remove them.

 

Avrum

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8 Replies
Moderator
Moderator
8,646 Views
Registered: ‎06-24-2015

Re: error : Place : 899

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Hi,

 

Refer to this AR:
http://www.xilinx.com/support/answers/24840.html

 

Thanks,
Nupur

Thanks,
Nupur
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Observer fatima06
Observer
8,641 Views
Registered: ‎11-03-2011

Re: error : Place : 899

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Thanks for you response. I've already seen this AR but I use a newer version of ISE (14.7) and this issue is not fixed. Also, if I want to work around by not using VRN/VRP as a IOB, I don't know the banks in the same column with the bank 22.

 

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Moderator
Moderator
8,639 Views
Registered: ‎02-16-2010

Re: error : Place : 899

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As the error message says, VRP/VRN pins of bank 3 are also used as user IOs. When DCI is used in any bank, these pins should be used to provide a reference resister for DCI circuit.

If your hardware has provided the reference resistors on VRP/VRN pins, please assign the signals locked to these pins to some other pins. It can resolve the error.
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Observer fatima06
Observer
8,636 Views
Registered: ‎11-03-2011

Re: error : Place : 899

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My design uses the majority of the IOBs of all the banks and so my IOBs are used as user IOs. Is it any other solution to keep all IOBs as user IOs and to use also DCI??

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Guide avrumw
Guide
8,616 Views
Registered: ‎01-23-2009

Re: error : Place : 899

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Do you understand what DCI is?

 

Digitally controlled impedance is a mechanism of calibrating the impedance of the drivers and termination resistors. Without calibration, the impedance of these devices is subject to the process/voltage/temperature variations that are inherant in all silicon processes - as a rule of thumb, this is roughly 3:1. This is generally acceptable for "slow" interfaces, but can be unacceptable to get the fastest possible interfaces.

 

If the 3:1 variation is acceptable to you, then don't use the DCI standards - all I/O standards that have a DCI version also have a non-DCI version, which can be used.

 

If you want to use DCI, though, these components need to be calibrated against a known reference impedance. This is done by connecting accurate resistors to the VRN and VRP pins of the FPGA - the DCI state machine then calibrates internal resistances using these external resistances as a reference. Without these references, the calibration cannot be done.

 

So, to use DCI in a bank you have two choices

  1) connect both the VRP and VRN pins to the reference resistors

  2) use the DCI_CASCADE to use the reference resistors in another bank in the same column of the FPGA

     - so there must still be at least one set of VRP/VRN resistors in the I/O column; there are two columns in most devices - some older families (V5, V6) had 3 or 4.

 

Avrum

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Observer fatima06
Observer
8,611 Views
Registered: ‎11-03-2011

Re: error : Place : 899

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Thank you for this detailed response. I want absolutely use DCI. I know which IOs in my bank should be connected to the references resistors but I don't know how to do it. I used this constraint " Inst pin-name DCI_VALUE = Integer" in my UCF but it doesn't work.

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Guide avrumw
Guide
16,433 Views
Registered: ‎01-23-2009

Re: error : Place : 899

Jump to solution

When you use DCI I/O in a bank, the tools have no way of knowing if you have placed the resistors on the appropriate pins. The only check it does is to make sure that there are no user I/O on the VRP and VRN pins. The message you are seeing seems to indicate that the tool thinks that there are user I/Os on at least one of the two VRP/VRN pins.

 

You don't need to and (as far as I know) there is no way to tell the tools that you are planning to connect the reference resistors to the VRP and VRN pins - just make sure the pins are not used for anything else (and, of course, be sure to actually connect the reference resistors on your board).

 

The DCI_VALUE attribute is only for IBIS generation, and should be applied to the IOB using DCI (not the VRP/VRN reference pin). In fact, it is possible that having this attribute on the VRP/VRN pins could confuse the tool into thinking that the pins are not available - you should remove them.

 

Avrum

View solution in original post

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Observer fatima06
Observer
8,581 Views
Registered: ‎11-03-2011

Re: error : Place : 899

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Thanks a lot for your help, that answers my question.

 

Fatima

 

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