SerialLite II

[Altera_Forum]

Hi, 

 I am trying the seriallite IP on the Stratix II GX signal integrity board and implement a loop back funtion with one TX and one RX. I found that when I disconnected only one of the differential signal of a TX lane. The RX still can work. I don't know why. Is that reasonale ?   Kent

[Altera_Forum]

Kent, 

 yes this is reasonable. A differential input essentially detects the crossing of the plus and minus inputs. If you disconnect an input, internal circuity may or will bias the this pin. This is often/always the case in AC-coupled connections. If the connected signal crosses this bias level the circuit will detect these crossings without distinction. It will probably suffer at higher bit rates, unless the connected signal is totally symmetric around the bias-level of the unconnected pin. Again if you have AC-coupling this will usually be the case.   Regards,  Josy

[Altera_Forum]

You may also start to see problems at different cable lengths. You're basically going to affect the equalizer's range of equalization (because you've messed with the signal amplitude). 

 Jake

[Altera_Forum]

Will the data be correct if only one line of the differential pair connect between TX and RX?