Solution

For more information on the Negative-Bias Temperature Instability (NBTI) of the Virtex-4 MGTs, refer to (Xilinx Answer 22471).

You can download a pcore example at:
http://www.xilinx.com/txpatches/pub/applications/misc/null_pair_example_v1_00_a.zip

MHS and UCF Examples

Virtex-4 FX20-FF672 MHS Top PORT definitions:
### MGT NULL TILES ####
PORT MGT102AB_TXN = MGT102AB_TXN, VEC = [1:0], DIR = O
PORT MGT102AB_TXP = MGT102AB_TXP, VEC = [1:0], DIR = O
PORT MGT102AB_RXN = MGT102AB_RXN, VEC = [1:0], DIR = I
PORT MGT102AB_RXP = MGT102AB_RXP, VEC = [1:0], DIR = I
PORT MGT105AB_TXN = MGT105AB_TXN, VEC = [1:0], DIR = O
PORT MGT105AB_TXP = MGT105AB_TXP, VEC = [1:0], DIR = O
PORT MGT105AB_RXN = MGT105AB_RXN, VEC = [1:0], DIR = I
PORT MGT105AB_RXP = MGT105AB_RXP, VEC = [1:0], DIR = I
PORT MGT113AB_TXN = MGT113AB_TXN, VEC = [1:0], DIR = O
PORT MGT113AB_TXP = MGT113AB_TXP, VEC = [1:0], DIR = O
PORT MGT113AB_RXN = MGT113AB_RXN, VEC = [1:0], DIR = I
PORT MGT113AB_RXP = MGT113AB_RXP, VEC = [1:0], DIR = I
PORT MGT110AB_TXN = MGT110AB_TXN, VEC = [1:0], DIR = O
PORT MGT110AB_TXP = MGT110AB_TXP, VEC = [1:0], DIR = O
PORT MGT110AB_RXN = MGT110AB_RXN, VEC = [1:0], DIR = I
PORT MGT110AB_RXP = MGT110AB_RXP, VEC = [1:0], DIR = I
Virtex-4 FX20-FF672 PCORE Instantiations:
### MGT NULL TILES ####
BEGIN null_pair_example
PARAMETER INSTANCE = MGT102AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT102AB_RXN
PORT rx1p = MGT102AB_RXP
PORT tx1n = MGT102AB_TXN
PORT tx1p = MGT102AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT105AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT105AB_RXN
PORT rx1p = MGT105AB_RXP
PORT tx1n = MGT105AB_TXN
PORT tx1p = MGT105AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT113AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT113AB_RXN
PORT rx1p = MGT113AB_RXP
PORT tx1n = MGT113AB_TXN
PORT tx1p = MGT113AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT110AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT110AB_RXN
PORT rx1p = MGT110AB_RXP
PORT tx1n = MGT110AB_TXN
PORT tx1p = MGT110AB_TXP
END
Virtex-4 FX20-FF672 UCF file Info:
##################################
### Virtex-4 FX20-FF672 MGT Null Tile LOCs ###
##################################
#LHS MGTs
#MGT102A
INST MGT102AB/*/GT11_INST_A/GT11_10GE_4_INST LOC = "GT11_X0Y3";
NET "MGT102AB_TXN<1>" LOC = "A23"; #TXN
NET "MGT102AB_TXP<1>" LOC = "A22"; #TXP
NET "MGT102AB_RXN<1>" LOC = "A20"; #RXN
NET "MGT102AB_RXP<1>" LOC = "A19"; #RXP
#MGT102B
INST MGT102AB/*/GT11_INST_B/GT11_10GE_4_INST LOC = "GT11_X0Y2";
NET "MGT102AB_TXN<0>" LOC = "A25"; #TXN
NET "MGT102AB_TXP<0>" LOC = "A24"; #TXP
NET "MGT102AB_RXN<0>" LOC = "D26"; #RXN
NET "MGT102AB_RXP<0>" LOC = "C26"; #RXP
#MGT105A
INST MGT105AB/*/GT11_INST_A/GT11_10GE_4_INST LOC = "GT11_X0Y1";
NET "MGT105AB_TXN<1>" LOC = "AC26"; #TXN
NET "MGT105AB_TXP<1>" LOC = "AB26"; #TXP
NET "MGT105AB_RXN<1>" LOC = "Y26"; #RXN
NET "MGT105AB_RXP<1>" LOC = "W26"; #RXP
#MGT105B
INST MGT105AB/*/GT11_INST_B/GT11_10GE_4_INST LOC = "GT11_X0Y0";
NET "MGT105AB_TXN<0>" LOC = "AE26"; #TXN
NET "MGT105AB_TXP<0>" LOC = "AD26"; #TXP
NET "MGT105AB_RXN<0>" LOC = "AF23"; #RXN
NET "MGT105AB_RXP<0>" LOC = "AF24"; #RXP
#RHS MGTs
#MGT113A
INST MGT113AB/*/GT11_INST_A/GT11_10GE_4_INST LOC = "GT11_X1Y3";
NET "MGT113AB_TXN<1>" LOC = "C1"; #TXN
NET "MGT113AB_TXP<1>" LOC = "B1"; #TXP
NET "MGT113AB_RXN<1>" LOC = "A3"; #RXN
NET "MGT113AB_RXP<1>" LOC = "A4"; #RXP
#MGT113B
INST MGT113AB/*/GT11_INST_B/GT11_10GE_4_INST LOC = "GT11_X1Y2";
NET "MGT113AB_TXN<0>" LOC = "E1"; #TXN
NET "MGT113AB_TXP<0>" LOC = "D1"; #TXP
NET "MGT113AB_RXN<0>" LOC = "H1"; #RXN
NET "MGT113AB_RXP<0>" LOC = "G1"; #RXP
#MGT110A
INST MGT110AB/*/GT11_INST_A/GT11_10GE_4_INST LOC = "GT11_X1Y1";
NET "MGT110AB_TXN<1>" LOC = "AF3"; #TXN
NET "MGT110AB_TXP<1>" LOC = "AF2"; #TXP
NET "MGT110AB_RXN<1>" LOC = "AD1"; #RXN
NET "MGT110AB_RXP<1>" LOC = "AC1"; #RXP
#MGT110B
INST MGT110AB/*/GT11_INST_B/GT11_10GE_4_INST LOC = "GT11_X1Y0";
NET "MGT110AB_TXN<0>" LOC = "AF5"; #TXN
NET "MGT110AB_TXP<0>" LOC = "AF4"; #TXP
NET "MGT110AB_RXN<0>" LOC = "AF8"; #RXN
NET "MGT110AB_RXP<0>" LOC = "AF7"; #RXP

Virtex-4 FX60-FF1152 MHS Top PORT definitions:
### MGT NULL TILES ####
PORT MGT113AB_TXN = MGT113AB_TXN, VEC = [1:0], DIR = O
PORT MGT113AB_TXP = MGT113AB_TXP, VEC = [1:0], DIR = O
PORT MGT113AB_RXN = MGT113AB_RXN, VEC = [1:0], DIR = I
PORT MGT113AB_RXP = MGT113AB_RXP, VEC = [1:0], DIR = I

PORT MGT112AB_TXN = MGT112AB_TXN, VEC = [1:0], DIR = O
PORT MGT112AB_TXP = MGT112AB_TXP, VEC = [1:0], DIR = O
PORT MGT112AB_RXN = MGT112AB_RXN, VEC = [1:0], DIR = I
PORT MGT112AB_RXP = MGT112AB_RXP, VEC = [1:0], DIR = I

PORT MGT110AB_TXN = MGT110AB_TXN, VEC = [1:0], DIR = O
PORT MGT110AB_TXP = MGT110AB_TXP, VEC = [1:0], DIR = O
PORT MGT110AB_RXN = MGT110AB_RXN, VEC = [1:0], DIR = I
PORT MGT110AB_RXP = MGT110AB_RXP, VEC = [1:0], DIR = I

PORT MGT109AB_TXN = MGT109AB_TXN, VEC = [1:0], DIR = O
PORT MGT109AB_TXP = MGT109AB_TXP, VEC = [1:0], DIR = O
PORT MGT109AB_RXN = MGT109AB_RXN, VEC = [1:0], DIR = I
PORT MGT109AB_RXP = MGT109AB_RXP, VEC = [1:0], DIR = I

PORT MGT102AB_TXN = MGT102AB_TXN, VEC = [1:0], DIR = O
PORT MGT102AB_TXP = MGT102AB_TXP, VEC = [1:0], DIR = O
PORT MGT102AB_RXN = MGT102AB_RXN, VEC = [1:0], DIR = I
PORT MGT102AB_RXP = MGT102AB_RXP, VEC = [1:0], DIR = I

PORT MGT103AB_TXN = MGT103AB_TXN, VEC = [1:0], DIR = O
PORT MGT103AB_TXP = MGT103AB_TXP, VEC = [1:0], DIR = O
PORT MGT103AB_RXN = MGT103AB_RXN, VEC = [1:0], DIR = I
PORT MGT103AB_RXP = MGT103AB_RXP, VEC = [1:0], DIR = I

PORT MGT105AB_TXN = MGT105AB_TXN, VEC = [1:0], DIR = O
PORT MGT105AB_TXP = MGT105AB_TXP, VEC = [1:0], DIR = O
PORT MGT105AB_RXN = MGT105AB_RXN, VEC = [1:0], DIR = I
PORT MGT105AB_RXP = MGT105AB_RXP, VEC = [1:0], DIR = I

PORT MGT106AB_TXN = MGT106AB_TXN, VEC = [1:0], DIR = O
PORT MGT106AB_TXP = MGT106AB_TXP, VEC = [1:0], DIR = O
PORT MGT106AB_RXN = MGT106AB_RXN, VEC = [1:0], DIR = I
PORT MGT106AB_RXP = MGT106AB_RXP, VEC = [1:0], DIR = I
Virtex-4 FX60-FF1152 MHS PCORE Instantiations:
### MGT NULL TILES ####
BEGIN null_pair_example
PARAMETER INSTANCE = MGT113AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT113AB_RXN
PORT rx1p = MGT113AB_RXP
PORT tx1n = MGT113AB_TXN
PORT tx1p = MGT113AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT112AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT112AB_RXN
PORT rx1p = MGT112AB_RXP
PORT tx1n = MGT112AB_TXN
PORT tx1p = MGT112AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT110AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT110AB_RXN
PORT rx1p = MGT110AB_RXP
PORT tx1n = MGT110AB_TXN
PORT tx1p = MGT110AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT109AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT109AB_RXN
PORT rx1p = MGT109AB_RXP
PORT tx1n = MGT109AB_TXN
PORT tx1p = MGT109AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT102AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT102AB_RXN
PORT rx1p = MGT102AB_RXP
PORT tx1n = MGT102AB_TXN
PORT tx1p = MGT102AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT103AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT103AB_RXN
PORT rx1p = MGT103AB_RXP
PORT tx1n = MGT103AB_TXN
PORT tx1p = MGT103AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT105AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT105AB_RXN
PORT rx1p = MGT105AB_RXP
PORT tx1n = MGT105AB_TXN
PORT tx1p = MGT105AB_TXP
END
BEGIN null_pair_example
PARAMETER INSTANCE = MGT106AB
PARAMETER HW_VER = 1.00.a
PORT clk = sys_clk_s
PORT rx1n = MGT106AB_RXN
PORT rx1p = MGT106AB_RXP
PORT tx1n = MGT106AB_TXN
PORT tx1p = MGT106AB_TXP
END
Virtex-4 FX60-FF1152 UCF file Info:
##################################
### Virtex-4 FX60-FF1152 MGT Null Tile LOCs ###
##################################
#MGT113A
INST MGT113AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X1Y7;
NET "MGT113AB_TXN<1>" LOC = "A3"; #TXN
NET "MGT113AB_TXP<1>" LOC = "A4"; #TXP
NET "MGT113AB_RXN<1>" LOC = "A6"; #RXN
NET "MGT113AB_RXP<1>" LOC = "A7"; #RXP
#MGT113B
INST MGT113AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X1Y6;
NET "MGT113AB_TXN<0>" LOC = "D1"; #TXN
NET "MGT113AB_TXP<0>" LOC = "C1"; #TXP
NET "MGT113AB_RXN<0>" LOC = "G1"; #RXN
NET "MGT113AB_RXP<0>" LOC = "F1"; #RXP
#MGT112A
INST MGT112AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X1Y5;
NET "MGT112AB_TXN<1>" LOC = "T1"; #TXN
NET "MGT112AB_TXP<1>" LOC = "R1"; #TXP
NET "MGT112AB_RXN<1>" LOC = "N1"; #RXN
NET "MGT112AB_RXP<1>" LOC = "M1"; #RXP
#MGT112B
INST MGT112AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X1Y4;
NET "MGT112AB_TXN<0>" LOC = "V1"; #TXN
NET "MGT112AB_TXP<0>" LOC = "U1"; #TXP
NET "MGT112AB_RXN<0>" LOC = "AA1"; #RXN
NET "MGT112AB_RXP<0>" LOC = "Y1"; #RXP
#MGT110A
INST MGT110AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X1Y3;
NET "MGT110AB_TXN<1>" LOC = "AG1"; #TXN
NET "MGT110AB_TXP<1>" LOC = "AF1"; #TXP
NET "MGT110AB_RXN<1>" LOC = "AD1"; #RXN
NET "MGT110AB_RXP<1>" LOC = "AC1"; #RXP
#MGT110B
INST MGT110AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X1Y2;
NET "MGT110AB_TXN<0>" LOC = "AJ1"; #TXN
NET "MGT110AB_TXP<0>" LOC = "AH1"; #TXP
NET "MGT110AB_RXN<0>" LOC = "AM1"; #RXN
NET "MGT110AB_RXP<0>" LOC = "AL1"; #RXP
#MGT109A
INST MGT109AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X1Y1;
NET "MGT109AB_TXN<1>" LOC = "AP10"; #TXN
NET "MGT109AB_TXP<1>" LOC = "AP9"; #TXP
NET "MGT109AB_RXN<1>" LOC = "AP7"; #RXN
NET "MGT109AB_RXP<1>" LOC = "AP6"; #RXP
#MGT109B
INST MGT109AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X1Y0;
NET "MGT109AB_TXN<0>" LOC = "AP12"; #TXN
NET "MGT109AB_TXP<0>" LOC = "AP11"; #TXP
NET "MGT109AB_RXN<0>" LOC = "AP15"; #RXN
NET "MGT109AB_RXP<0>" LOC = "AP14"; #RXP
#MGT102A
INST MGT102AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X0Y7;
NET "MGT102AB_TXN<1>" LOC = "E34"; #TXN
NET "MGT102AB_TXP<1>" LOC = "D34"; #TXP
NET "MGT102AB_RXN<1>" LOC = "A32"; #RXN
NET "MGT102AB_RXP<1>" LOC = "A31"; #RXP
#MGT102B
INST MGT102AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X0Y6;
NET "MGT102AB_TXN<0>" LOC = "G34"; #TXN
NET "MGT102AB_TXP<0>" LOC = "F34"; #TXP
NET "MGT102AB_RXN<0>" LOC = "K34"; #RXN
NET "MGT102AB_RXP<0>" LOC = "J34"; #RXP
#MGT103A
INST MGT103AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X0Y5;
NET "MGT103AB_TXN<1>" LOC = "W34"; #TXN
NET "MGT103AB_TXP<1>" LOC = "V34"; #TXP
NET "MGT103AB_RXN<1>" LOC = "T34"; #RXN
NET "MGT103AB_RXP<1>" LOC = "R34"; #RXP
#MGT103B
INST MGT103AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X0Y4;
NET "MGT103AB_TXN<0>" LOC = "AA34"; #TXN
NET "MGT103AB_TXP<0>" LOC = "Y34"; #TXP
NET "MGT103AB_RXN<0>" LOC = "AD34"; #RXN
NET "MGT103AB_RXP<0>" LOC = "AC34"; #RXP
#MGT105A
INST MGT105AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X0Y3;
NET "MGT105AB_TXN<1>" LOC = "AK34"; #TXN
NET "MGT105AB_TXP<1>" LOC = "AJ34"; #TXP
NET "MGT105AB_RXN<1>" LOC = "AG34"; #RXN
NET "MGT105AB_RXP<1>" LOC = "AF34"; #RXP
#MGT105B
INST MGT105AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X0Y2;
NET "MGT105AB_TXN<0>" LOC = "AM34"; #TXN
NET "MGT105AB_TXP<0>" LOC = "AL34"; #TXP
NET "MGT105AB_RXN<0>" LOC = "AP31"; #RXN
NET "MGT105AB_RXP<0>" LOC = "AP32"; #RXP
#MGT106A
INST MGT106AB/*/GT11_INST_A/GT11_10GE_4_INST LOC=GT11_X0Y1;
NET "MGT106AB_TXN<1>" LOC = "AP22"; #TXN
NET "MGT106AB_TXP<1>" LOC = "AP23"; #TXP
NET "MGT106AB_RXN<1>" LOC = "AP25"; #RXN
NET "MGT106AB_RXP<1>" LOC = "AP26"; #RXP
#MGT106B
INST MGT106AB/*/GT11_INST_B/GT11_10GE_4_INST LOC=GT11_X0Y0;
NET "MGT106AB_TXN<0>" LOC = "AP20"; #TXN
NET "MGT106AB_TXP<0>" LOC = "AP21"; #TXP
NET "MGT106AB_RXN<0>" LOC = "AP17"; #RXN
NET "MGT106AB_RXP<0>" LOC = "AP18"; #RXP