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Harald Welte laforge at gnumonks.orgHi Christian,
On Sat, Dec 24, 2011 at 10:47:09PM +0100, Christian Vogel wrote:
> >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.
Sorry, I'm not going to change back now ;)
> 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.
ok, I'll look at that. The pin-configuratoin of the TDM connector is
definitely not
> 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.
Well, I think for SPI there is no speed requirement anyway (it's just
configuring the transceiver and maybe reading an error status back), so
if there are problems, we can simply reduce the clock rate.
For the TDM signals, they are 2MBits/s and there is nothing we can
change about that ;)
I'll see if I can squeeze in some resistor footprints there.
> >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.
If it wasn't for the router, I could have done the project in KiCAD,
where from my experience routing is really bad and/or takes ages.
> I'll try my luck on manually > routing the new board tomorrow in the
> morning or so...
Don't bother, it's a waste of time. Really. I've already spent way too
much time on this and would say it's about time to order some actual
PCBs (seeedstudio.com 9.99 for 10 units and cheapest shipping option)
and play with it.
I'll probably render some GErber output, look at it in a gerber viewer
and order tomorrow or on the 26th.
> 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.
I think E1 is not specified over that distance anyway. Last time I
checked, it was in the low hundreds of meters.
> 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).
Yes, you're probably right. But let's try not to over-optimize this.
We're talking about a development board which will probably be produced
and used in a quantity of one or two dozen.
If later somebody emerges with a microcontroller/fpga/cpld design that
does something useful with the transceiver (i.e. implement an actual
functional E1 interface with HDLC, etc.), it would make a lot of sense
to make a custom board with this external logic and the transceiver on
one board.
Regards,
Harald
--
- Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/
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