LVDS_E_1R and LVDS_E_3R are modes that emulate LVDS output using other I/O buffers instead of dedicated LVDS output buffers.
 
For example, if you run out of dedicated LVDS outputs, you can use LVDS input channels as output channels.
 
Please note the following points when using it.
About LVDS_E_1R
・A Resistor Network (1 resistor) is required near the FPGA.
・The supported device family is
HardCopy III/IV, Stratix III/IV
About LVDS_E_3R
・A Resistor Network (three resistors) is required near the FPGA.
・The supported device family is
HardCopy III/IV, Stratix III/IV, Arria II GX, Cyclone III/IV
 
For details, search for the keyword "Resistor Network" in the Device Handbook of each device and refer to it.