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The I/O standard for QDRII+ : HSTL-I inputs and variable drive HSTL-I output buffers.
It supports both 1.5 V and 1.8 V I/O supply
As you said the input IOstandrad is HSTL_I and output IOStandard is HSTL_DCI_I(Variable) .
As the given formula for the resistance the
input R = RQ/3.33 , i have taken the RQ = 250 ohms then
Rinput =75 ohms
output R = RQ/5 then
Routput = 50 ohms
The output resistance of the memory or the input resistance of the FPGA internal.
As given reference schematic design in WEB the output does not have the output resistance
QDR II+ support HSTL-I i/o standard. For outputs, the impedance can be varied.
RQ/3.3 determines the on-die termination resistance on the input pins. You can select ODT low range and have this value almost equal to 50 ohms.
For the output resistance is RQ/5. It is correct. The output resistance are in build to the memory . In the knowledge article the output does not have any output resistance in that schematic the input is having the resistance.
Reference Schematic Design Recommendation for QDR-DDR II/II+/Xtreme SRAMs - KBA84386