>
> Hello all
>
> I am considering to make a temperature probe using a PIC microcrontroller of
> some sort. This probe should be able to 'speak' SNMP, both GET and SET.. I
> have seen a few products claiming to add TCP/IP support to uC's, but most of
> them uses RS232 to a modem or something else. What I'd really like is a
> device with ethernet, capable of getting av IP via DHCP, and serve SNMP
> request. Anyone ever done this, or have links to something even remotely
> similar?
>
> I guess it would neet to support 802.2, ARP, DHCP, IP, UDP, SNMP and
> possibly DNS.
>

Frankly ethernet just isn't a real convenient medium in terms of board space,
pin space, ram required, or processor capacity. All the protocols you
describe are perfectly capable of running on multidrop serial requiring only
an 8 pin interface chip and a serial interface to hook up. I currently have
two of my students working on a multidrop RS485 network using UDP/SLIP as
the transport protocol. We haven't yet tested if it's possible to map multiple
IP's onto a single SLIP interface yet though. Our gateway is a standard
Linux box.

However if you really want ethernet let me throw out three possible
suggestions for physical connectivity. Software/Protocol stacks you'll have
to figure out on your own:

1) Parallel port ethernet. A device such as a D-Link 620. They can be had for
relatively cheap, and almost gurantee to have a 4 pin parallel interface
for communication requiring only 9 or 10 pins to interface to the PIC. One
suggestion is to make sure to pick up a device that has a Linux driver because
then you can use the Linux kernel source code to derive the communications
protocol.

2) The RealTek 8019 chipset. This particular chipset has a real simple 8 bit
memory mapped interface mode and contains the buffer RAM required to buffer
the packets. Problem is that the part is a QTFP surface mount and so will
require some skill to actually interface with your project.

3) Use a ISA ethernet card. Most of the existing Ethernet interface projects
take this route. There is at least one published article in CircuitCellar
INK that describes a 8051 type uC interfaced to a NE2000 card.

But it's still my contention that you'll end up spending a significant
amount of time and energy getting the physical interface working no matter
which route you take. And none of the proposed solutions above invites a
small physical footprint with the smallest footprint (#2) being the most
difficult to achieve. Both of the others will occupy at least 10 in^2.

So let me offer as a final suggestion to work out your protocol stacks using
a serial interface and SLIP, then tackle the ethernet issue once the board's
software is stable and tested. Then you won't get caught up in the testing
issue of trying to determine if it's the driver interface code, or the
protocol interface code that's causing the system not to work.

Good Luck.

BAJ

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