Hi Harald,
I've not yet looked at your updated design, just finished the Christmas
celebrations with relatives and so on ;-)...
I've meanwhile updated the design
(last night) to actually place two RJ45 sockets, one in TE and one in NT
mode.
I would go with the jumper-selectable method, but that's maybe just
personal preferance.
The TDN / RDN are not differential signals, if
that's what you're
thinking of.
Indeed, that's what I thought of, nevertheless I'd try to have at least
the clock lines somewhere adjecent to ground, even if it's only based on
my gut feeling.
> I don't know about the intended cable lengths,
but maybe a few series
> resistors for dampening the signal wouldn't hurt.
You're referring to which signals?
SPI and TMS, if you have fast outputs on either the E1 transceiver or the
microcontroller/fpga, series resistors (say... 68 Ohm) might dampen the
ringing on the edges.
I'm not sure how easy that is, I've already
spent a lot of time with the
layout to make sure the autorouter doesn't produce complete crap. So
in order to conserve time, I may not be doing that.
I never used the eagle autorouter, because I think it doesn't produce
elegant routing, or sometimes no routing at all. Fortunately all my boards
were of comparably low complexity (one microcontroller, maybe one or two
small
additional ICs, everything low pin-count). I'll try my luck on manually
routing the new board tomorrow in the morning or so...
I was thinking about a BAV99 (it's used on
HFC-E1), but the IDT data
sheet specifically specifies one diode type, and it has very different
characteristics (200mV less forward voltage, ...) than the BAV99.
I checked the datasheet and they use rather strong (500mA and up) schottky
diodes (hence the lower forward drop compared to the BAV99).
Possibly they are considering their product being connected in a commercial
telco-equipment with a few kilometres of cable connected to it, and the
diodes are for protecting the inputs from overvoltage.
Personally, I'd say that for the current design you can easily go with
a little weaker diodes, such as the BAT54s (dual in SOT23 smd) which
can take up to 200mA (avg).
Greetings from bavaria,
Chris