R7 and R8 are optional. These spare footprints allow option of amplitude  attenuation if needed.  AC couple capacitors C1 and C2 values are frequency dependence. (Value can  be range from 100pF to 0.1uF)  

Signal at the HCSL input:  Typical Offset = 0.35V (Cross Point)  Typical Swing Amplitude = 0.7V (or 1.4V differential), for R7=0 ohms, R8=0 ohms.