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'PICs in simple Ethernet applications'
1998\03\01@141416 by Dr. Rich Artym

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I opened up some antique Adacom fanout boxes the other day and found
some nice mini switchmode PSUs and lots of LEDs and Ethernet sockets
with their own pulse xformers and bit-repeater circuitry.  Aha, I
thought, toyboxes for networked PICs! :-)

However, it brought some questions to mind.  There's no chance of a
bare PIC keeping up with Ethernet bit rates, especially bearing in mind
the sync problems, but it must be possible to put some fast hardware up
front to relax the timing requirement.  I don't have any specific use
in mind, but I am curious as to what's possible and what's not, cheaply.
(Putting an Ethernet controller in there defeats the whole idea.)

Fairly simply, a long shift register could be used to capture passing
Ethernet frames on a one-shot basis (only one frame accepted until the
PIC releases the interlock).  All the paraphenalia of CSCD/MA can be
ignored on input because the CRC will be incorrect if a collision
spoils the frame, and the PIC can easily check that in its own time.
[Or, to keep costs low, it might be possible to use a double-buffered
8 or 16-bit shift register and use the PIC to parallel-load it into
an external memory buffer on the fly -- tight timing, but not too bad.]

Something like that could form the basis of, at the very least, yet
another PIC programmer :-), albeit networked, or an interesting home
automation module for those wiring their homes up with Ethernet.

I've drawn a bit of a blank so far on net searches in this general
area, ie. PICs in Ethernet-related applications.  If anyone has come
across any such, or has ideas on how PICs might handle fast networking
simply (full IP stack not required!), I'd love to hear about it.

Cheers,

Rich.

1998\03\01@173219 by Robert Walker

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       Instead of using an Ethernet controller for projects such
       as home automation, why not get hold of a simple terminal
       server such as Digital Equipment Corporations - DECSERVER 200,
       these units provide up to 8 modem controlled serial ports and
       link back to an ethernet controller.

       Most of these units are outdated, and can be picked up for
       almost nothing. However, they provide up to 8 ports and can
       communicate from 300 to 19.2kbps, and the output of the
       ethernet port is DEC LAT, which is fairly well defined.

       Infact, if you are really into it you can in theory reprogram
       them, as I believe they are MC68000 with a chunk of memory and
       a few UARTS and an ethernet port. The DECSERVER 200 downloads
       its software via the network, thus all that would be required
       would be a idea of the internals of the server and a suitable
       cross compiler/linker etc (Does any onw have such info?). You
       would then need a system to down load the image, a PC or a DEC
       system of some sort and you have a customized 8 unit
       controller interface.

       Or, if you have access to a DEC System (i.e. VAX/VMS, Alpha
       VMS, PDP etc), you could using the DEC software connect a
       session from that machine directly to a terminal server port
       and cut out all the hardwork.

       All of this is easy to PIC up these days, as terminal servers
       are cheap, VAX systems are on the second hand market.

       Just a though anyway.

Rob.

1998\03\01@200551 by Dr. Rich Artym

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In message <C347IGS1T9D8*/R=A1/R=A1CBR/U=WALKER_R/@MHS>, Rob writes:

> Instead of using an Ethernet controller for projects such
> as home automation, why not get hold of a simple terminal
> server such as Digital Equipment Corporations - DECSERVER 200,
> these units provide up to 8 modem controlled serial ports and
> link back to an ethernet controller.

Thanks for your comments Rob, but ...

That's not a solution simply because it would cost a small fortune
to put terminal servers all over one's house, or even just one per
room with the RS232 providing the fanout in each room.  Indeed, it
makes no sense to buy an expensive interfacing unit just because
the PIC can handle RS232 rates but not Ethernet ones directly.
[Using surplus is OK for a handful of people, but it doesn't scale.]

That's what motivated my query:  OK, so we can't expect Cisco-type
performance and full IP networking all done within a PIC, but it's
certainly able to do frame decoding and encoding offline and to hand
frames to fast but cheap external hardware for delivery at Ethernet
rates.

The question is, what kind of minimal external KISS hardware needs
to be placed in front of the PIC to give it a fighting chance?  And,
what would the consequent tradeoffs in performance and capability be?
Those seem quite interesting questions.  Anyone can design systems
around application-specific VLSI building blocks -- just follow the
application notes.  It seems much more creative (and lots more fun)
to seek out "alternative" designs though when the requirements allow
it, and the PIC is a wonderful component for those that enjoy such
creativity.

Remember the Cheap Video Cookbook?  I'm not at all surprised to hear
that Don Lancaster now likes PICs.

Cheers,

Rich.

1998\03\01@203831 by Eric Smith

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"Dr. Rich Artym" <spam_OUTrartymTakeThisOuTspamGALACTA.DEMON.CO.UK> wrote:
> However, it brought some questions to mind.  There's no chance of a
> bare PIC keeping up with Ethernet bit rates, especially bearing in mind
> the sync problems, but it must be possible to put some fast hardware up
> front to relax the timing requirement.  I don't have any specific use
> in mind, but I am curious as to what's possible and what's not, cheaply.
> (Putting an Ethernet controller in there defeats the whole idea.)

Rich Ottosen and I have discussed this from time to time.  Even running the
PIC at the maximum rated speed, the amount of external hardware needed to
provide hardware assist for Ethernet will cost more than a complete
Ethernet chip.  The receive side is the more difficult, and requires a PLL
for clock recovery and a Manchester decoder, in addition to a shift register.
The bit stuffing could potentially be done in software.

A simple Ethernet chip like the Crystal Semiconductor CS8900 is very
inexpensive and does not require many other components.  It has enough
internal memory for two Ethernet frames, and the host interface is simple.
It should be possible to use this with a PIC to implement a simple network
node.

Even with the Scenix part in turbo mode at 50 MHz (20 nS per instruction),
Ethernet would still require substantial external support hardware if a
standard Ethernet chip was not used.

SMC also makes a simple Ethernet chip like the CS8900, but I don't know the
part number.

Cheers,
Eric

1998\03\01@204250 by William Chops Westfield

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   OK, so we can't expect Cisco-type performance and full IP networking all
   done within a PIC, but it's certainly able to do frame decoding and
   encoding offline and to hand frames to fast but cheap external hardware
   for delivery at Ethernet rates.

Thanks for the plug.

Ethernet "controllers" come in approximately three flavors:

1) full-feature high speed controllers with built-in DMA and/or bus
  controllers  (ie AMD LANCE.)

2) byte-delivery devices with only a FIFO (ie SEEQ 8003.)  As used in
  several generations of cisco routers (with external microprogrammed
  bitslice to do everything in (1), plus additional stuff.

3) ISA-PC oriented controllers with independent buffer memory (National
  8390x series and "reference design".

The last of these is most suited to front-ending a PIC, I think.  The
orignal design was for ISA 8bit slots which are also too slow to
actually handle ethernet speed traffic, so the PC would stuff data off
into an 8k buffera and then say "go", and vis-versa.  An extra data copy
(evil stuff for a high speed router), but just the thing for slow
processors.

The integration rate has stepped up, of course, and now the single chip
controllers contain built-in 10baseT tranceivers, IEEE802.mumble
compatible network managment capabilities, etc, etc, but you can easilly
find 8bit ethernet cards based on the original 8390 ("Novell type 1", I
think) for less than $20 (unused), now that everyone wants PCI, 100Mbps,
and so on...

Note that without built-in 10baseT or thinnet tranceivers, you may be
paying nearly as much to connect a plain ethernet card to your net as
you would for an rs232 port into one of the cheaper (non-cisco :-)
ethernet terminal servers (10baseT external xceiver, some fraction of a
hub box, etc.)

BillW
cisco

1998\03\01@211008 by rrose

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> Rich Ottosen and I have discussed this from time to time.  Even running the
> PIC at the maximum rated speed, the amount of external hardware needed to
> provide hardware assist for Ethernet will cost more than a complete
> Ethernet chip.  The receive side is the more difficult, and requires a PLL
> for clock recovery and a Manchester decoder, in addition to a shift register.
> The bit stuffing could potentially be done in software.
>
> A simple Ethernet chip like the Crystal Semiconductor CS8900 is very
> inexpensive and does not require many other components.  It has enough
> internal memory for two Ethernet frames, and the host interface is simple.
> It should be possible to use this with a PIC to implement a simple network
> node.
>
> Even with the Scenix part in turbo mode at 50 MHz (20 nS per instruction),
> Ethernet would still require substantial external support hardware if a
> standard Ethernet chip was not used.
>
> SMC also makes a simple Ethernet chip like the CS8900, but I don't know the
> part number.

Another option could be to use CAN (Controller Area Network) instead
of Ethernet.

Richard Rosenheim
remove $$$ to reply

1998\03\02@160950 by SHAWN ELLIS

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Can I get the consensus of opinion on the best PIC programmer to buy
out there?

It needs to be able to program at least the  16C74 and 16C5X.  So I
want it to be able program several varieties of PICs.  And I prefer
NT compatibility/RS232 interface.

So, give me your 2 cents worth everybody!

1998\03\03@034841 by Dr. Rich Artym

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In message <.....19980302013450.23768.qmailKILLspamspam@spam@brouhaha.com>, Eric Smith writes:

> A simple Ethernet chip like the Crystal Semiconductor CS8900 is very
> inexpensive and does not require many other components.  It has enough
> internal memory for two Ethernet frames, and the host interface is simple.
> It should be possible to use this with a PIC to implement a simple network
> node.

Many thanks for this info -- I hadn't come across this controller before.
Looking at the specs on the net, the level of integration is about as
high as it can get, literally a one-chip solution.  If "very inexpensive"
means down in single figures, this would transform the situation totally.
I'll start looking around for UK distributors.

Cheers,

Rich.

1998\03\03@035003 by Dr. Rich Artym

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In message <199803020212.SAA18760spamKILLspambighorn.accessnv.com>, Richard Rosenheim
writes:

> Another option could be to use CAN (Controller Area Network) instead
> of Ethernet.

Well, not in my case because I'm looking for Ethernet connectivity, but
it could be of interest in other situations.  I have an interest in kit
cars as well so I've had a look at CAN bus chips before.  The prices of
CAN microcontrollers are ridiculously high though: 70 to 200 pounds for
an 8051 with integrated CAN bus support --- yikes!  8 quid for a CAN bus
I/O device though, so that's not too bad, in the PIC ballpark.

Cheers,

Rich.

1998\03\03@035005 by Dr. Rich Artym

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In message <.....CMM.0.90.4.888802884.billwKILLspamspam.....flipper.cisco.com>, BillW writes:

> Thanks for the plug.

Your're welcome -- deservedly so.  At work, the company spends millions
on Cisco kit every year and almost everyone seems happy, so credit where
credit is due.  [I said *almost* everyone -- I'm having to fight the
Cisco Local Director (an address rewriting bridge, for those that aren't
in the ISP business) every day, and my happiness factor is quite low,
but that's another story. :-)]  For the purposes of this list, I mentioned
Cisco only as an example of a company that implements its Ethernet well.

{Quote hidden}

Good info.  Alas, none of these are really one-chip solutions and not
even the 8390 is particularly cheap as I recall (cheap in the PIC sense)
except in very large quantities.

> you can easilly find 8bit ethernet cards based on the original 8390
> ("Novell type 1", I think) for less than $20 (unused), now that everyone
> wants PCI, 100Mbps, and so on...

Maybe I'll end up doing what so many others do, ie. riding on the
shoulders of the PC market by adding an ISA slot into the design. Bleh.
[Unless the Crystal CS8900 turns out to be really cheap.]

Cheers,

Rich.

1998\03\03@114338 by Keith Howell

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Someone mentioned how expensive 8051 chips with integrated CAN are.

I built a 16-bit CANbus I/O node for controlling a pneumatic valve
block. This used an 80C32, DIP ROM, 24C02, and a 82C200 CAN chip.
This was a lot cheaper than the integrated chips, which often have more
I/O (such as ADCs on the 82C592) than you wish to pay for.

I also arranged the I/O so you still had access to the TTL serial port
for running BASIC-52 diagnostic programs (external MAX202 adapter
needed). Very handy for impressing customers who think you've written a
BASIC interpreter in three days!

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