Xilinx SelectIO 7 Series User Manual page 33

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
termination circuit to the mid-point V
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. For more details, see IN_TERM in
UG625: Constraints Guide (for the ISE® tools) or UG912: Vivado Design Suite Properties
Reference Guide.
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:
Table 1-7
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
HSTL_II
HSTL_I_18
HSTL_II_18
I
SSTL18_
SSTL18_II
7 Series FPGAs SelectIO Resources User Guide
UG471 (v1.10) May 8, 2018
Uncalibrated Split Termination in High-Range I/O Banks (IN_TERM)
and the other to ground, providing a Thevenin equivalent
CCO
NET "pad_net_name"IN_TERM = "UNTUNED_SPLIT_50";
shows a list of I/O standards that support the IN_TERM constraint in the HR
DIFF_HSTL_I
DIFF_HSTL_II
DIFF_HSTL_I_18
DIFF_HSTL_II_18
DIFF_SSTL18_I
DIFF_SSTL18_II
www.xilinx.com
/2. The termination is present constantly on
CCO
SSTL15_R
SSTL15
SSTL135_R
SSTL135
DIFF_SSTL15_R
DIFF_SSTL15
DIFF_SSTL135_R
DIFF_SSTL135
33
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