On Jun 9, 2010, at 4:59 PM, Isaac Marino Bavaresco wrote:

> was doing some research on Embedded Ethernet and found some
> interesting results that may be useful to others:
>
> 1) Micro-controllers with embedded 10/100 Ethernet controllers  
> implement
> only the MAC, you will need an external PHY.

Not universally true.  For instance, the Freescale (coldfire) MCF5223x  
include an integrated 10/100 PHY, as do (all?) of the TI Stellaris  
(ARM) chips.

> 2) 10/100 MAC only available in 32-bit devices.

Sorta irrelevant, since a non-32bit device would be hard-pressed to  
output more than 10Mbps anyway, and the switch it's connected to will  
convert as appropriate...

> 3) To interface to a PHY it is necessary either 10 (RMII) or 18 (MII)
> pins, all but three exclusive to the PHY. The other three can be  
> shared
> with other PHYs if you have more MACs in the MCU.
> 4) Micro-controllers with otherwise identical characteristics are  
> around
> $0.27 cheaper without Ethernet.
> 5) PHY chips cost around $3.98 @ 1 or $3.54 @ 100.

Yes, the phy is annoying.  Also a power-hungry bit of silicon, usually.


> 6) a - ENC424J600 is a complete 10/100 Ethernet controller (MAC+PHY).
>    b - Costs around $4.56 @ 1, $3.58 @ 10, $3.29 @ 25 and $2.98 @ 100.
>    c - Can be interfaced with the MCU either with 4 pins (SPI) or 12  
> or
> more pins (parallel), most of which can be shared with other devices.

Also the Wiznet chips with embedded TCP/IP code, at somewhat similar  
prices.


> 7) Most MCUs with embedded Ethernet have only one MAC, some rare (very
> big) ARM MPUs have two

I'm not sure I'd say "rare"; there's a rather big "small router"  
market serviced by such chips, generally with MIPS, ARM, or PPC  
cores.  I'll go along with "big", and probably "not common in the  
hobbyist space" (unless you want to count all those mods to COTS  
routers...)

BillW

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