4.1.1. QSF Assignments for Reference Clock Pins
| Description | Value | QSF Assignment | 
|---|---|---|
| Set reference clock IO standard | differential LVPECL | set_instance_assignment -name IO_STANDARD "DIFFERENTIAL LVPECL" -to <refclk_name> -entity <block_name> | 
| Enable on-die termination resistors |   enable_term = (on-chip termination on) disable_term = (on-chip termination off)  |  
       set_instance_assignment -name HSSI_PARAMETER "refclk_divider_enable_termination=enable_term" -to ref_clk[0]  Recommendation: Set this to enable_term unless external on-board termination is used and internal termination is supposed to be bypassed.  |  
     
| Select 3.3 V tolerant instead of 2.5 V |   enable_3p3v_tol = (3.3V) disable_3p3v_tol = (2.5V)  |  
       set_instance_assignment -name HSSI_PARAMETER "refclk_divider_enable_3p3v=enable_3p3v_tol" -to ref_clk[0] 35  Recommendation: Set this to disable_3p3v_tol unless the clock source is compliant to LVPECL 3.3v standard.  |  
     
| Enable LVPECL driver hysteresis |   enable_hyst = (hysteresis on) disable_hyst = (hysteresis off)  |  
       set_instance_assignment -name HSSI_PARAMETER "refclk_divider_disable_hysteresis=enable_hyst" -to ref_clk[0]  Recommendation: Set this to disable_hyst provided that the reference clock characteristic meets the specification in the Device Data Sheet.  |  
     
| Set reference clock frequency | freq_in_Hz = "legal value" |  set_instance_assignment -name HSSI_PARAMETER "refclk_divider_input_freq=freq_in_Hz" -to ref_clk[0]  Recommendation: Use the same reference clock frequency number as in the respective transceiver IP.  |  
     
| Power down LVPECL driver |   false = (driver on) true = (driver off)  |  
       set_instance_assignment -name HSSI_PARAMETER "refclk_divider_powerdown_mode=false" -to ref_clk[0]  Recommendation: If you plan to use the target reference clock, set this to false.  |