Receiver VREF Scan in HP I/O Banks

UltraScale Architecture SelectIO Resources User Guide (UG571)

Document ID
UG571
Release Date
2022-08-31
Revision
1.14 English

An optional VREF scan feature in HP I/O banks helps to fine tune the internal VREF 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. VREF scan requires building control logic into your interconnect logic design.

Figure 1-16:      Connection from the Interconnect Logic to Access the VREF Scan Feature

X-Ref Target - Figure 1-16

X16074-connection-from-the-interconnect-logic-to-access-the-vref-scan-feature.jpg

Internal VREF tuned using the VREF scan feature controls the VREF 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 VREF are possible within a bank (for four byte groups in each bank). However, to use this feature, the central VREF of the bank needs to be set using the INTERNAL_VREF attribute (See Internal VREF). Inputs with I/O standards of different VREF specifications cannot be placed within the same bank. Tuned VREF connection (VREF output of HPIO_VREF primitive) cannot traverse byte group boundaries.

Figure 1-17:      VREF Scan Connection per Byte Group within a Bank

X-Ref Target - Figure 1-17

X16075-vref-scan-connection-per-byte-group-within-a-bank.jpg

Internal VREF (INTERNAL_VREF and VREF scan) cannot be combined with external VREF usage within a bank.

VREF_CNTR is used with the HPIO_VREF UNISIM primitive to set the VREF 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 VREF scan feature is invoked. The FABRIC_VREF_TUNE[6:0] port is used to tune the VREF from the interconnect logic. The approximate value of VREF 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 VREF Value as a Result of Using the VREF Scan Function

FABRIC_TUNE_VREF[6:0]

VREF (% of VCCO)

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%