Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

SerialLite II

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

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    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's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    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's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

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