Uncalibrated Input Termination in I/O Banks

UltraScale Architecture SelectIO Resources User Guide (UG571)

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

The HR I/O and HP I/O banks have an optional uncalibrated input on-chip split-termination feature for HSTL and SSTL standards and a single-termination feature for POD and HSUL standards that are similar to the DCI feature. This option creates a Thevenin equivalent circuit using two internal resistors of twice the target resistance value (2R where R = Z0) for HSTL and SSTL standards. One resistor terminates to VCCO and the other to GND, providing a Thevenin equivalent termination circuit of half the resistor value to the mid-point VCCO/2 for HSTL and SSTL standards. A single resistor terminates to VCCO for POD and HSUL standards.

The termination is present constantly on inputs, and on bidirectional pins whenever the output buffer is 3-stated except when DCITERMDISABLE (in HP I/O banks) or INTERMDISABLE (in HR I/O banks) are asserted. However, an important difference between this uncalibrated option and DCI is that instead of calibrating to an external reference resistor on the VRP pin when using DCI, the uncalibrated input termination feature invokes internal resistors determined by the ODT attribute that have no calibration routine to compensate for temperature, process, or voltage variations.

Possible ODT values for split-termination standards (HSTL and SSTL) are RTT_40, RTT_48, RTT_60, or RTT_NONE.

Possible values for ODT for single-termination POD standards are RTT_40, RTT_48, RTT_60, or RTT_NONE.

Possible values for ODT for single-termination HSUL standards are RTT_120, RTT_240, or RTT_NONE.

The main difference in how DCI or uncalibrated termination is invoked in a design is whether or not a DCI I/O standard is chosen. In both DCI and uncalibrated I/O standards, the values of the termination resistors are determined by the ODT attribute.

Table: I/O Standards that Support Uncalibrated Termination  shows a list of I/O standards that support the uncalibrated termination in both the HR and HP I/O banks.

Table 1-7:      I/O Standards that Support Uncalibrated Termination 

HSTL_I

DIFF_HSTL_I

SSTL18_I

DIFF_SSTL18_I

POD12

DIFF_POD12

HSTL_II

DIFF_HSTL_II

SSTL18_II

DIFF_SSTL18_II

POD10

DIFF_POD10

HSTL_I_18

DIFF_HSTL_I_18

SSTL15_R

DIFF_SSTL15_R

HSUL_12

DIFF_HSUL_12

HSTL_II_18

DIFF_HSTL_II_18

SSTL15

DIFF_SSTL15

 

 

 

 

SSTL135_R

DIFF_SSTL135_R

 

 

 

 

SSTL135

DIFF_SSTL135

 

 

 

 

SSTL12

DIFF_SSTL12