The in28J60 is a stand-alone Ethernet controller module with an industry
standard Serial Peripheral Interface (SPI).
It is part of the
Modtronix Presto iMod product range.
It has a RJ45 connector with built in magnetics, LEDs
and PoE circuitry. The module has press-fit connectors for easy integration onto a target board,
with no soldering required. It can be mounted on a custom board, a prototype board (like Veroboard),
or one of our
Presto SBC Boards.
The RJ45 connector allows power to be obtained via the network cable from either the two used
pairs (pins 1,2,3 and 6), or the two unused pairs (4,5,7 and 8), as defined by the Power Over
Ethernet (PoE) standard. Provision is also made for a custom, cheaper implementation of PoE by
routing power from the unused network pairs (4,5,7 and 8), via a diode, to the Auxiliary power pin of
the module. This Auxiliary power can be used to power the target board (board is mounted on). For
details, download datasheet below.
For details on ENC28J60, dowload it's datasheet from www.microchip.com.
The in28J60 is part of the Modtronix
The in28J60 has two rows of press-fit connectors on the bottom of the board.
They can be pressed into 1.00mm holes on a 1.6mm thick (standard PCB thickness) target board.
No special tool is required, they can be inserted by applying firm pressure to the connectors.
Once fitted to the target board, the board is very secure, and can not be removed by hand any more.
A screwdriver or similar tool can be used to remove the board if required. If the in28J60 is to be soldered onto the target board, 1.10mm holes can be used. This will allow it to be inserted
much easier than with 1.00mm holes. When using 1.10mm holes, the board can be removed by hand.
Official IEEE 802.3af PoE Implementation
The official IEEE 802.3af Power over Ethernet standard provides 48 volts DC over two of
the four available pairs of the network cable with a maximum current of 400 mA, for a
maximum load power of 15.4 W. The circuit required to convert this to 5V or 3.3V (done
on PD – Powered Device) is quite complex and expensive. It is not implemented by
this module! All four signals, that is POE+1,
POE-1, POE+2 and POE-2, are required to implement IEEE 802.3af. This is because the PSE
(Power Sourcing Equipment, like a switch that provided PoE for example) can provide power
on either POE-1 and POE+2, or POE-2 and POE+2 according to the standard. The X1U and X2U
connectors have to be assembled to get access to these signals. They are not assembled by
default, as can be seen in picture above.
Proprietary PoE Implementation
A cheap and simple alternative to the official IEEE 802.3af implementation is to use the
spare pairs of the network cable (pins 4,5,7 and 8 of network connector) for power.
There are many commercial products available that use this method. An injector is
required to put the power (normally 12V or 24V) on the network cable. This injector
is normally located at the switch, and will place power on all cables that require it.
The PD (powered devices) on the other end of the cable can than use this module to access the
supply voltage on the network cable.
The figure below shows the circuitry that extracts power from the spare
cable pairs. The signals are marked POE+2 and POE-2 in the schematic.
The POE-2 signal (pins 4 and 5 of network connector) is routed to ground via solder
jumper J3. This solder jumper is made by default. The POE+2 signal is routed to the
Vaux pin on the X1 press-fit connector, via a 40V, 1A Schottky diode. Power sent
via the spare pair on the network cable can thus be obtained via the GND and Vaux
pins of the X1 and X2 press-fit connectors.