Using the Arduino Ethernet shield with AMICUS18 (Joint forum project?)
Hi,
With this post I hope to spark the interest in what could develop into a joint forum project. The purpose of the project is to get the Arduino Ethernet shield working with the AMICUS18 board and, of course PBP.
Unfortunately the Ethernet shield isn't very directly compatible with the AMICUS18. The reason for this is that the shield picks up the SPI signals used to communicate with the W5100 ethernet chip and the onboard SD-card from the ICSP programming header on the Arduino. For apparent reasons this header does not exist on the AMICUS18. This means that Ethernet shield needs to be modifed in order to use it and this first post of mine is going to cover what and how I did to make it work with the AMICUS18.
Before I go on I'd like to point out a couple of things:
1) I'm using Ethernet shield v.6 which I got from NKC electronics, so what I describe here applies to that particular version. I do not know how it'll work with previous (or upcomming) versions of the shield.
2) Doing these modification most likely voids any warranty you might have on the Ethernet shield.
3) You do it at your own risk, don't blame me if you mess it up.
As have been said the Ethernet shield uses a SPI interface to communicate with the host CPU. Since these signals are brought to the ICSP header on the shield we need to "move" them to pins that suits us better. The 18F25K22 that is used on the AMICUS18 has its SPI signals on RC3, 4 & 5 which are the same as pins 4, 3 & 2 on the Ethernet shield. Now, moving the SPI signals from the ICSP header to RC3, 4 & 5 wouldn't be too hard but unfortunately two out of three pins (RC3 & RC5) are already in use by the shield so we need to move those signals too - before we can connect the SPI signals to these I/O's.
Pin 2 on the Ethernet shield (RC5 on the AMICUS18) carries the interrups signal from the W5100 chip. Since we might want to use this signal later on it would make sense to move it to an I/O-pin of the 18F25K22 capable of generating an interrupt. I've selected RB0 which on the Ethernet shield is labeled AREF. Fortunately AREF is not connected to anything on the shield so we're good to go there. By default the W5100 interrupt signal isn't actually connected to Pin2, instead there are two small solder pads on the back of the board which, when bridged with solder, connects the signal to Pin2. We'll use one of these pads to "hijack" the signal and re-route it to RB0 instead.
Pin4 on the Ethernet shield carries the chip select signal for the onboard micro-SD card socket. This signal is an ordinary I/O so any pin will do really. I've selected RB2 which, on the Ethernet shield, is labeled 13.
Why not RB1 you may think. It's because RB1 on the shield is GND and it would be hard to gain access to that pin without serious board surgury. This also brings up an important point: On the AMICUS18 board there's jumper that allows you the select if RB1 should "be" RB1 or if it's GND. This jumper should be in the GND location.
When these two signals are moved we can connect the SPI interface signals from the 2X3 ICSP header to pins 2, 3 and 4 on the shield. Let's start with the trickiest one, Pin4, which carries the chip select signal for the SD-Card. First we need to "disconnect" the signal from Pin4, this is done by cutting the PCB trace just where it comes out from under the Arduino logo:
With the trace cut we can turn the board over and find a good spot to "tap into" the signal:
Running a wire from the via marked SD_SC to RB2 and a wire from the pad marked W5100_INT to RB0 is all it takes to "free up" the AMICU18's SPI pins so we can use them.
In the next photo I've marked which pins in the ICSP header that we're interested in. SCK goes to RC3, MISO goes to RC4 and MOSI goes to RC5. I opted to remove the header altogether because it has a slight interference with the socket for the 18F25K20 on the AMICUS18 board.
Here's the the back of the board with the modification complete. One trace cut and five jumper wires and we should be good to go. (I guess you can't really call that "Arduino shield compatible"....)
/Henrik.
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