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7 Series FPGAs SelectIO Resources User Guide www.xilinx.com 75
UG471 (v1.5) May 15, 2015
Supported I/O Standards and Terminations
bidirectional signals (no input-only or output-only). HR banks provide IN_TERM options
for untuned internal parallel split-termination resistors. Although the optimal drive and
termination scheme for any new design is determined through careful signal-integrity
analysis, initial considerations include:
• HP I/O banks: SSTL15_T_DCI at the 7 series FPGAs bidirectional pins (DQ and DQS),
and SSTL15 at the unidirectional pins (all other pins). ODT used at the memory device
on the bidirectional signals, and external parallel-termination resistors to
V
TT
=V
CCO
/2 for the unidirectional signals.
• HR I/O banks: SSTL15 at the 7 series FPGAs pins for both bidirectional (DQ/DQS)
and unidirectional (all other pins) signals, combined with the IN_TERM (internal
termination) attribute on the bidirectional pins. Use ODT at the memory device on the
bidirectional signals, and external parallel-termination resistors to V
TT
=V
CCO
/2 for
the unidirectional signals.
SSTL135 is used for DDR3L SDRAM memory interfaces and is roughly defined (not by
name) in the JEDEC standard JESD79-3-1. For this standard, the full-strength driver
(SSTL135) is available in both the HP and HR I/O banks. A weaker, reduced-strength
driver, designated by an R in the standard name (SSTL135_R), is available in the HR I/O
banks. Both drivers support bidirectional and unidirectional signaling. For some
topologies (such as short point-to-point interfaces), the reduced-strength driver can result
in reduced overshoot and better signal integrity.
The HP I/O banks also provide DCI and T_DCI options for tuned internal parallel
split-termination resistors. While the DCI option is not available for bidirectional signals
(input or output only), the T_DCI option is only available for bidirectional signals (no
input-only or output-only). HR banks provide IN_TERM options for untuned internal
parallel split-termination resistors. Although the optimal drive and termination scheme
for any new design is determined through careful signal-integrity analysis, initial
considerations include:
• HP I/O banks: SSTL135_T_DCI at the 7 series FPGAs bidirectional pins (DQ and
DQS), and SSTL135 at the unidirectional pins (all other pins). ODT used at the
memory device on the bidirectional signals, and external parallel-termination
resistors to V
TT
=V
CCO
/2 for the unidirectional signals.
• HR I/O banks: SSTL135 at the 7 series FPGAs pins for both bidirectional (DQ/DQS)
and unidirectional (all other pins) signals, combined with the IN_TERM (internal
termination) attribute on the bidirectional pins. Use ODT at the memory device on the
bidirectional signals, and external parallel-termination resistors to V
TT
=V
CCO
/2 for
the unidirectional signals.
SSTL12 supports Micron's next-generation RLDRAM3 memory. This standard is only
available in the HP I/O banks. Both DCI and T_DCI options are available to improve the
signal integrity through the use of tuned internal split-termination resistors. While the DCI
option is not available for bidirectional signals (input or output only), the T_DCI option is
only available for bidirectional signals (no input-only or output-only). Although the
optimal drive and termination scheme for any new design is determined through careful
signal-integrity analysis, initial considerations include:
• SSTL12_T_DCI at the 7 series FPGAs bidirectional pins (DQ and DQS)
• SSTL12 at the unidirectional pins (all other pins).
• ODT used at the memory device, if available on the bidirectional signals, and external
parallel-termination resistors to V
TT
=V
CCO
/2 where ODT is not available.
- 7 Series FPGAs 1
- SelectIO Resources 1
- Revision History 2
- Table of Contents 5
- UG471 (v1.5) May 15, 2015 10
- About This Guide 11
- Preface: About This Guide 12
- New Features 14
- 7 Series FPGA I/O Bank Rules 17
- Introduction 19
- Xilinx DCI 20
- DCIRESET Primitive 22
- DCI Cascading 22
- DCI and 3-state DCI (T_DCI) 28
- DCI Usage Examples 31
- IBUF and IBUFG 35
- IBUF_IBUFDISABLE 35
- IBUF_INTERMDISABLE 36
- IBUFDS and IBUFGDS 36
- IBUFDS_DIFF_OUT_IBUFDISABLE 37
- IBUFDS_IBUFDISABLE 37
- IBUFDS_INTERMDISABLE 38
- IBUFDS_DIFF_OUT_INTERMDISABLE 38
- IOBUF_DCIEN 39
- IOBUF_INTERMDISABLE 40
- IOBUFDS_DCIEN 41
- IOBUFDS_DIFF_OUT 42
- IOBUFDS_DIFF_OUT_DCIEN 43
- IOBUFDS_INTERMDISABLE 44
- DCI_CASCADE Constraint 46
- Location Constraints 47
- IOSTANDARD Attribute 47
- IBUF_LOW_PWR Attribute 47
- Output Slew Rate Attributes 48
- VCCAUX_IO Constraint 50
- LVTTL (Low Voltage TTL) 51
- LVCMOS (Low Voltage CMOS) 54
- LVDCI _ DV2 57
- HSLVDCI (High-Speed LVDCI) 59
- HSTL_ I and HSTL_ I_18 60
- HSTL_I_12 60
- HSTL_ II and HSTL_ II_18 60
- N/A Available 62
- External Termination 63
- Differential HSTL Class I 64
- HSTL Class II 66
- Differential HSTL Class II 68
- Not 3-stated 72
- (T pin logic Low) 72
- 3-stated 72
- (T pin logic High) 72
- SSTL18_I, DIFF_SSTL18_I 76
- DIFF_SSTL135 76
- User Guide for details 77
- HSUL_12 and DIFF_HSUL_12 84
- Example Board Topology 85
- Differential HSUL_12 86
- MOBILE_DDR (Low Power DDR) 88
- Transmitter Termination 91
- Receiver Termination 91
- Differential Clock 93
- Input to the FPGA 93
- BLVDS (Bus LVDS) 96
- Table 1-55: V 99
- Chapter 1: SelectIO Resources 102
- SelectIO Logic Resources 105
- ILOGIC Resources 106
- ZHOLD_DELAY 108
- OPPOSITE_EDGE Mode 109
- SAME_EDGE Mode 110
- SAME_EDGE_PIPELINED Mode 110
- Input DDR Resources (IDDR) 111
- ILOGIC Timing Models 112
- Clock Event 4 113
- Clock Event 1 113
- Clock Event 9 114
- IDELAYE2 Primitive 115
- IDELAY Ports 116
- IDELAYRESOLUTION 117
- IDELAY Attributes 118
- IDELAY Modes 119
- IDELAY Timing 120
- Clock Event 2 121
- Clock Event 3 121
- Clock Event 0 122
- IDELAYCTRL 123
- IDELAYCTRL Timing 124
- IDELAYCTRL Locations 124
- OLOGIC Resources 125
- Output DDR Overview (ODDR) 126
- Clock Forwarding 127
- Output DDR Primitive (ODDR) 128
- OLOGIC Timing Models 128
- Timing Characteristics 129
- ODELAYE2 Primitive 133
- ODELAY Ports 134
- ODELAY Attributes 136
- ODELAY Modes 137
- ODELAY Timing 138
- Chapter 3 141
- ISERDESE2 143
- Primitive 143
- Registered Outputs – Q1 to Q8 144
- Combinatorial Output – O 145
- Bitslip Operation - BITSLIP 145
- High-Speed Clock Input - CLK 146
- High-Speed Clock Input - CLKB 146
- Divided Clock Input - CLKDIV 146
- Oversampling Mode - OCLK 147
- Reset Input - RST 147
- ISERDESE2 Attributes 148
- DATA_RATE Attribute 149
- DATA_WIDTH Attribute 149
- INTERFACE_TYPE Attribute 149
- ISERDESE2 Clocking Methods 150
- MEMORY Interface Type 151
- MEMORY_QDR Interface Type 151
- OVERSAMPLE Interface Type 151
- ISERDESE2 Width Expansion 153
- OSERDESE2 154
- BITSLIP Submodule 156
- After Clock Event 3 158
- OSERDESE2 Primitive 160
- Data Path Output - OQ 161
- DATA_RATE_OQ Attribute 163
- DATA_RATE_TQ Attribute 163
- SERDES_MODE Attribute 164
- TRISTATE_WIDTH Attribute 164
- OSERDESE2 Width Expansion 165
- Output Feedback 166
- OSERDESE2 Latencies 166
- IO_FIFO Overview 171
- FIFO Core 172
- 7 Entries Deep 172
- Register Register 172
- IN_FIFO Primitive 173
- Table 3-15: IN_FIFO Ports 174
- OUT_FIFO 175
- OUT_FIFO Primitive 176
- Table 3-18: OUT_FIFO Ports 177
- Resetting the IO_FIFO 178
- EMPTY and FULL Flags 178
- Termination Options for 181
- SSO Noise Analysis 181
- TMDS_33 Far 3.3V 50Ω 183
- IO Standard 183
- Default Termination 183
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