Turn your EasyPic2 development board into an ENC28J60 Ethernet Toolkit
You will be surprised to see how simple it is !
The EasyPic2 : A good candidate for this enhancement
This is good old EasyPic2 development board from MikroElektronika. But it is still healthy and does a lot of good job. For those who don't know this board, here is a little review of its main features :
- On-board USB fast programmer
- DIP8 to DIP40 PIC sockets
- 32 LEDs and 32 buttons, connected to I/O pins
- 4 digits 7 segments LED display
- Socket for 2x16 LCD text display
- 2 trimmers for A/D conversion
- 5 connectors, directly connected to I/O pins with pull-up/pull-down resistor arrays
- RS232 adaptor and connector
There was space left on the board, so MikroElektronika had the good idea to make a prototype area for users.
210 plated-trough holes, both sides solder mask : until this day I never used this area.
210 plated-trough holes, both sides solder mask : until this day I never used this area.
On the back side, we see that the upper row is connected to the +5V power line, and the lower row to the ground line.
Good ! Nature hates empty spaces isn't it ? Me too !
What do we need ?
Almost all that you need is on this picture. The heart of the circuit is the ENC28J60 Microchip Serial Ethernet Adapter, it is now widely available, and its DIP28 package is very convenient for prototyping.Other important part is the 3.3V voltage regulator (transistor-like 3-pins plastic case on the picture) : the ENC28J60 can't operate directly with the +5V provided by the board.
The 25 Mhz crystal for ENC28J60 clock is easy to find at your usual supplier.
You will have also to find a magnetic for ethernet network (black rectangular box left to the RJ-45 socket), this one comes from an old ethernet hub board, as well as other parts seen on this picture. There are now RJ-45 sockets with integrated LEDs and magnetic, if you want to save more space on your board.
And now, go shopping :
| Quantity | Part # or value | Type |
|---|---|---|
| 1 | ENC28J60 (Microchip) | Serial Ethernet Controller |
| 1 | LP2950CZ-3.3 | +3.3V voltage regulator |
| 1 | 25 MHz | crystal |
| 1 | Green | LED |
| 1 | Red | LED |
| 1 | 10 µF 25V | capacitor |
| 1 | 47 µF 25V | capacitor |
| 2 | 10 nF | capacitor |
| 2 | 15 pF | capacitor |
| 1 | 100 nF | capacitor |
| 1 | 1 nF 2KV | capacitor |
| 4 | 50 Ohm 1% | precision resistor |
| 1 | 2.7 K 1% | precision resistor |
| 2 | 470 Ohm | resistor |
| 1 | FB2022 | TX/RX magnetic filter |
| 1 | ferrite bead (value not critical) | inductor |
| 1 | DIP 28 pins | IC socket |
| 1 | RJ45 | female solderable socket |
| 1 | 2x5 pins connector + 5 jumpers | used as switch |
The circuit schematic
The circuit schematic comes from the datasheet of the ENC28J60 :http://ww1.microchip.com/downloads/en/DeviceDoc/39662a.pdf
As you can see, it is pretty simple :
The ENC controller is connected to the network through a magnetic adapter.
It needs a 25 Mhz crystal for its internal clock, resistors & capacitors for terminations, a 2.7K bias resistor, and a 10 µF capacitor to stabilize its internal 2.5V power supply.
The controller can directly drive two programmable LEDs through current limitation resistors.
It is connected to the PIC through a 5 lines bus : reset line (RESET), chip select line (CS), SPI clock (CLK), SPI data input (SI), SPI data output (S0).
There are also 2 control lines that are not used in this exemple, but you can add them if you want, they are the interrupt line (INT) and the wake up on lan line (WOL). They can be used to trigger PIC interrupts, but in this example we operate using the polling method and we don't need them.
The most frequently asked question about this controler is the voltage level adaptation. The controller operates at 3.3V and the PIC on the board operates at 5.0V.
So, the question is : how to adapt ENC voltage levels to PIC voltage level ?
We must consider both sides :
PIC output voltage for logical 1 is 5V : does ENC accepts 5V on its inputs, whereas it is 3.3V powered ?
The answer is yes, ENC inputs are 5V compliant, so that there is no risk for the controller to apply 5V on its inputs, and they will correspond to logical 1.
ENC output voltage for logical 1 is 3.3V : will the inputs of the PIC turn high or low when 3.3V coming from the ENC outputs is applied ?
The answer is : it depends on the inputs of the PIC. TTL inputs give logical 1 above 2.05V, and will not require voltage level shifting. Schmitt trigger inputs give logical 1 above 3.5V, and will require voltage level shifting.
In fact, we can consider that if we connect ENC outputs to PIC TTL inputs only, the voltage level adapter is... a wire.
Most of PICs have TTL inputs and integrated SPI on PORTC, so we will connect all ENC line to this port.
Assembly
After soldering, you should get something that looks like this :
As you can see, I used a red/green bicolor LED instead of the two LEDs.
The jumper socket is placed just in front of the five lines that are connected to the PIC, so that removing the jumper isolates the ethernet circuit from the PIC, and PORTC can be used for other purposes.
The 3.3V regulator is mounted on a tulip socket : I have only one for now, and it is shared with another test board.
The 25 Mhz crystal is also mounted on a tulip socket, to save place for the two 15 pF capacitors hidden behind.
I'm a little bit ashamed, but I show you the back side anyway. Sorry for the mess ;-)
Take care to respect the receive circuit polarity, because ENC is not able to detect it correctly due to a silicon bug. That's why I used color wires. If you connect it wrong, you may either have receive problem, or no receive at all.
The bus is connected to the PORTC pins of the DIP28 socket.
Note that my cable deserves to be shortened...
Finally, this is what it looks like :
| Front side | Back side |
 |  |
Testing the Ethernet board with a source code example
It's time ! First, check and double-check all connections.
Don't plug the ENC28J60 in its socket, then power the board and verify the 3.3V power supply on each pin of the ENC.
Then turn the board off, put a 40 pins PIC as a PIC16F877A or a PIC18F452 in its socket, and clock it at its maximum speed.
Plug the ENC28J60 in its socket, and set the fiver jumpers to enable bus line between PIC and ENC.
Get complete code
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