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7 Series FPGAs SelectIO Resources User Guide www.xilinx.com 33
UG471 (v1.5) May 15, 2015
Uncalibrated Split Termination in High-Range I/O Banks (IN_TERM)
Uncalibrated Split Termination in High-Range I/O Banks (IN_TERM)
The HR I/O banks have an optional on-chip split-termination feature very similar to the
3-state split-termination DCI feature available in the HP I/O banks. Similar to the 3-state
split-termination DCI in the HP banks, the option in the HR banks creates a Thevenin
equivalent circuit using two internal resistors of twice the target resistance value. One
resistor terminates to V
CCO
and the other to ground, providing a Thevenin equivalent
termination circuit to the mid-point V
CCO
/2. The termination is present constantly on
inputs, and on bidirectional pins whenever the output buffer is 3-stated. However, an
important difference between this uncalibrated split-termination option and 3-state
split-termination DCI is that instead of calibrating to external reference resistors on the
VRN and VRP pins when using DCI, this feature invokes internal resistors that have no
calibration routine to compensate for temperature, process, or voltage variations. This
option has target Thevenin equivalent resistance values of 40Ω, 50Ω, and 60Ω.
Another difference from the DCI termination is how this uncalibrated termination is
invoked in a design. While the 3-state split-termination DCI option is invoked by assigning
the T_DCI I/O standards to I/O pins in HP I/O banks, the uncalibrated split-termination
option is invoked by assigning IN_TERM constraints to the I/O pin nets in HR I/O banks.
This can be done in several ways, including in the source HDL design, in the UCF, NCF, or
XCF files, or in the PlanAhead™ software. See “In Term” in UG625
: Constraints Guide for
more details.
In HR banks, the IN_TERM constraint can be set to NONE (default),
UNTUNED_SPLIT_40, UNTUNED_SPLIT_50, or UNTUNED_SPLIT_60. An example of
the UCF syntax is:
NET "pad_net_name"IN_TERM = "UNTUNED_SPLIT_50";
Table 1-7 shows a list of I/O standards that support the IN_TERM constraint in the HR
I/O banks. IN_TERM is not supported in HP I/O banks.
Table 1-7: I/O Standards that Support IN_TERM
HSTL_I DIFF_HSTL_I SSTL15_R DIFF_SSTL15_R
HSTL_II
DIFF_HSTL_II SSTL15 DIFF_SSTL15
HSTL_I_18
DIFF_HSTL_I_18 SSTL135_R DIFF_SSTL135_R
HSTL_II_18 DIFF_HSTL_II_18
SSTL135 DIFF_SSTL135
SSTL18_I DIFF_SSTL18_I
SSTL18_II DIFF_SSTL18_II
- 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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