Honored Contributor
Honored ContributorThe fact you can transmit a totally arbitrary sequence is not related by the tool, but on how electrically you connect the transmitter and the receiver.
If the links are AC connected, you NEED to use a balanced protocol because else the Capacitor at some point is fully charged. An example maybe clarify a little bit. Suppose you transmit a very long sequence of '1', at that point you'll have that the capacitor is fully charged, now if you want to transmit only a single '0' and then continue with the 1 sequence that means you of course on the receiver side do not see it, because that only single zero last to few times in order to discharge the capacitor to a level that is seen as '0' by the receiver. This is always more true more frequencies are higher. I hope it clarify a little bit. Ok now the other issue: all 1 or all 0. Serdes has to recover clock and that is done from the data transitions. If data do not have transition you cannot recover the clock. Moreover if you transmit all time 0 or 1, you could use a TTL line :) Another issue is that once the clock is recovered (and it depend from PLL time, first it lock to clock reference you provide and then he start to lock to data) you can imagine that receiver start to see an infinite sequence of 1 and 0 but depending on its locked time, receiving board turn on time respect sending board and other, he need a way to understand where are the boundaries of these bits that he is receiving, told in another way which is the first bit that has to be used to fill the word registers of the widht you specified. Ok I hope it is a bit clearer now, in any case you can have a look at http://www.altera.com/education/training/curriculum/high-speed_io/trn-high-speed_io.html Have a look at TRANSCEIVER BASIC course on that page These are online FREE course from Altera web site: They are very nice done imo. You can find them from www.altera.com then go on learning section and then training course :)
