An optional V
REF
scan feature in HP I/O banks helps to fine tune the internal V
REF
of input buffers to maximize the performance for a subset of I/O standards. This feature can be accessed through the IBUFE3 and IOBUFE3 primitives in conjunction with the HPIO_VREF primitive as shown in
This Figure
. V
REF
scan requires building control logic into your interconnect logic design.
Figure 1-16:
Connection from the Interconnect Logic to Access the V
REF
Scan Feature
|
X-Ref Target - Figure 1-16
|
Internal V
REF
tuned using the V
REF
scan feature controls the V
REF
of 13 consecutive I/Os (1 byte group) within a bank as shown in
This Figure
. There are four byte groups within a bank. Four different variations of a given V
REF
are possible within a bank (for four byte groups in each bank). However, to use this feature, the central V
REF
of the bank needs to be set using the INTERNAL_VREF attribute (See
Internal V
REF
). Inputs with I/O standards of different V
REF
specifications cannot be placed within the same bank. Tuned V
REF
connection (V
REF
output of HPIO_VREF primitive) cannot traverse byte group boundaries.
Figure 1-17:
V
REF
Scan Connection per Byte Group within a Bank
|
X-Ref Target - Figure 1-17
|
Internal V
REF
(INTERNAL_VREF and V
REF
scan) cannot be combined with external V
REF
usage within a bank.
VREF_CNTR is used with the HPIO_VREF UNISIM primitive to set the V
REF
scan-range based on the I/O standard.
The valid values for the VREF_CNTR attribute are described in this section.
•
FABRIC_RANGE1 (POD standards)
•
FABRIC_RANGE2 (other applicable standards)
FABRIC_RANGE1 is used with the POD standards and the FABRIC_RANGE2 is used with the other applicable standards when the receiver V
REF
scan feature is invoked. The FABRIC_VREF_TUNE[6:0] port is used to tune the V
REF
from the interconnect logic. The approximate value of V
REF
for various values in reference to FABRIC_VREF_TUNE and VREF_CNTR is shown in
Table: Approximate VREF Value as a Result of Using the VREF Scan Function
.
Table 1-11:
Approximate V
REF
Value as a Result of Using the V
REF
Scan Function
|
FABRIC_TUNE_VREF[6:0]
|
V
REF
(% of V
CCO
)
|
|
VREF_CNTR = FABRIC_RANGE1
|
VREF_CNTR = FABRIC_RANGE2
|
|
000 0001
|
58.00%
|
43.00%
|
|
000 0010
|
58.50%
|
43.50%
|
|
000 0011
|
59.00%
|
44.00%
|
|
000 0100
|
59.50%
|
44.50%
|
|
000 0101
|
60.00%
|
45.00%
|
|
000 0110
|
60.50%
|
45.50%
|
|
000 0111
|
61.00%
|
46.00%
|
|
000 1000
|
61.50%
|
46.50%
|
|
000 1001
|
62.00%
|
47.00%
|
|
000 1010
|
62.50%
|
47.50%
|
|
000 1011
|
63.00%
|
48.00%
|
|
000 1100
|
63.50%
|
48.50%
|
|
000 1101
|
64.00%
|
49.00%
|
|
000 1110
|
64.50%
|
49.50%
|
|
000 0000
|
65.00%
|
50.00%
|
|
000 1111
|
65.50%
|
50.50%
|
|
001 0000
|
66.00%
|
51.00%
|
|
001 0001
|
66.50%
|
51.50%
|
|
001 0010
|
67.00%
|
52.00%
|
|
001 0011
|
67.50%
|
52.50%
|
|
001 0100
|
68.00%
|
53.00%
|
|
001 0101
|
68.50%
|
53.50%
|
|
001 0110
|
69.00%
|
54.00%
|
|
001 0111
|
69.50%
|
54.50%
|
|
001 1000
|
70.00%
|
55.00%
|
|
001 1001
|
70.50%
|
55.50%
|
|
001 1010
|
71.00%
|
56.00%
|
|
001 1011
|
71.50%
|
56.50%
|
|
001 1100
|
72.00%
|
57.00%
|
|
001 1101
|
72.50%
|
57.50%
|
|
001 1110
|
73.00%
|
58.00%
|
|
001 1111
|
73.50%
|
58.50%
|
|
010 0000
|
74.00%
|
59.00%
|
|
010 0001
|
74.50%
|
59.50%
|
|
010 0010
|
75.00%
|
60.00%
|
|
010 0011
|
75.50%
|
60.50%
|
|
010 0100
|
76.00%
|
61.00%
|
|
010 0101
|
76.50%
|
61.50%
|
|
010 0110
|
77.00%
|
62.00%
|
|
010 0111
|
77.50%
|
62.50%
|
|
010 1000
|
78.00%
|
63.00%
|
|
010 1001
|
78.50%
|
63.50%
|
|
010 1010
|
79.00%
|
64.00%
|
|
010 1011
|
79.50%
|
64.50%
|
|
010 1100
|
80.00%
|
65.00%
|
|
010 1101
|
80.50%
|
65.50%
|
|
010 1110
|
81.00%
|
66.00%
|
|
010 1111
|
81.50%
|
66.50%
|
|
011 0000
|
82.00%
|
67.00%
|
|
011 0001
|
82.50%
|
67.50%
|
|
011 0010
|
83.00%
|
68.00%
|
|
011 0011
|
83.50%
|
68.50%
|
|
011 0100
|
84.00%
|
69.00%
|
|
011 0101
|
84.50%
|
69.50%
|
|
011 0110
|
85.00%
|
70.00%
|
|
011 0111
|
85.50%
|
70.50%
|
|
011 1000
|
86.00%
|
71.00%
|
|
011 1001
|
86.50%
|
71.50%
|
|
011 1010
|
87.00%
|
72.00%
|
|
011 1011
|
87.50%
|
72.50%
|
|
011 1100
|
88.00%
|
73.00%
|
|
011 1101
|
88.50%
|
73.50%
|
|
011 1110
|
89.00%
|
74.00%
|
|
011 1111
|
89.50%
|
74.50%
|
|
100 0000
|
90.00%
|
75.00%
|
|
100 0001
|
90.50%
|
75.50%
|
|
100 0010
|
91.00%
|
76.00%
|
|
100 0011
|
91.50%
|
76.50%
|
|
100 0100
|
92.00%
|
77.00%
|
|
100 0101
|
92.50%
|
77.50%
|
|
100 0110
|
93.00%
|
78.00%
|
|
100 0111
|
93.50%
|
78.50%
|
|
100 1000
|
94.00%
|
79.00%
|
