Variable drive HSTL output buffer

Question: What does Variable drive HSTL output buffer means?



An external resistor, RQ, must be connected between the ZQ pin on the SRAM and VSS to allow the SRAM to adjust its output driver impedance. The value of RQ must be 5X the value of the intended line impedance driven by the SRAM, The allowable range of RQ to guarantee impedance matching is between 175 and 350 thus varying output impedance between 35 ohms and 70 ohms.