[Ronja] Twister2 U63-U65
twibright at hispeed.ch
Fri Apr 4 19:17:34 BST 2008
---- Sordrag at gmx.de schrieb:
> Hi all!
> I'm trying to understand how the Twister works. My problem is the cascade of U63 to U65 (and also the one of U51 and U53). I don't get the idea behind this. I already read the FAQs but they were not enough.
The idea is that if a fast signal is pulse extended then the individual pulses blur
together and create a steady level. If a slow one is pulse extended they don't blur
and stay as a frequency.
> Can anyone explaine me in detail how the identification of data in the signal by the use of the cascades works?
U54 is just a buffer. C66 and R52 replace leading edges in the signal with short
H impulses and everything else with L. U52 inverts it and on every leading edge of the
original signal, U63 gets reset to zeroes on all outputs. On every tick of the 16MHz clock (62.5 ns) one tap
gets set to one. That means if the output is on the 5th tap, it gets set from
0 back to 1 after 4-5 ticks, that means after 250-312.5 ns it gets back to H.
If the incoming signal has the leading edge pitch less than 250ns, then the output stays
permanently in 0. If it has more, then it will contain ones interspersed with zeroes.
The Manchester signal has maximum leading edge pitch of 200ns. The silence between
the packets takes at least 9600ns. So packets will produce zero on U63-10 and the interframe gaps one.
The problem is link integrity pulses will trigger a false packet alarm. Therefore U64 and U65 are there to clean this out.
> And why is there the OR (U54) before this cascade? It just works as an inverter and the signal gets inverted back thru U52. Is this necessary?
> And why are there after the RX discriminator (U51, U53) those two Schmitt Triggers of U52. I think if I do the hole cicuit on a PCB I have short wires so those Triggers aren't necessary!?
The Schmitt trigger inverters are there to invert the signal. Their Schmitt function
> Thx for your help.
> Greetz Sord
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