Ethernet on the G120

NETMF & Gadgeteer
1

Looking at the preliminary pinout for the G120 module I see no ethernet pins.
However looking at the datasheet for the cortex-m3 processor i see that it has a ethernet controller.
And assuming the pin names are the same on both the Cortez and the G120, it’s obvious that the pins for ethernet have been laid out.
But the pins are an RMII protocol so I would need a driver IC, to turn that into something that I can connect to a RJ45 plug.

can someone confirm this? Or have I completely misunderstood something.

Greetings Morten Hedegaard

2

You will need to add ENC28J60 chip, which will cost you same as adding a Ethernet PHY.

3

But wouldn’t it be more beneficial to use the built-in ethernet controller, instead of using SPI. Espicially when the pins are already available?

4

Not everyone needs ethernet. The module seems better suited for graphics / handheld applications.
But maybe, if there are enough requests, GHI will build a G120-E which is directed more to ethernet users.
I think GHI was wise to “keep it simple” for a start.

5

Not really considering everything evolved. You only need 3 SPI pins (can still be used) vs using over 10 pins if using PHY. You will have a simpler design and no worries about high frequency of MAC signals, which not everyone understand how to handle. You will probably save on cost. The only negative thing it is a little slower.

6

G120-E is EMX so this already exists :slight_smile:

Actually G120 is very well suited for networking. WiFi uses SPI and it works with G120 and using SPI based ethernet will make your design better. Probably even better to pass FCC/CE since you are not worried about MAC signals.

7

Fair enough. It is a lot simpler with just SPI.

8

Hello,

Old topic, but I am wondering what ethernet speed rate can we hope with ENC28 + G120 module ? 10 Mbps, or 100Mbps? What is the limiting factor? SPI link or other?

Cheers,

9

cca,
ENC28j60 is a 10baseT (10Mbits) chip, so this is maximum speed it can reach.
I think that SPI will be very stressed at higher rate, specially if it is shared for other peripheral on spi bus.

Microchip has also ENC24J600 that is faster and use 100Mbits, but I haven’t seen around any driver for ARM world.

10

Internal eth on most chip Nxp, Atmel and STM32 for example can manage that. But using MII or RMII internal module costs lot of pin and you need a phy external chip in any case.
Mountaneer has a driver for internal MII of the stm32 CPU.