Toradex Colibri - Colibri Ethernet Port Configuration

Colibri Carrier Board Design Guide
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2.2 Ethernet
The Colibri module standard features a fast 10/100Mbit Ethernet (10/100Base-TX) interface port.
The required center tap circuit can differ between the modules. Different assembly options might
be needed for supporting the complete Colibri module family. Some modules support Auto MDIX,
which means they can swap the transmitting with the receiving lanes. Read the corresponding
datasheet of the module for more information about the availability of the Auto MDIX function.
2.2.1 Ethernet Signals
Colibri
Pin
Colibri
Signal Name
I/O
Type
Power
Rail
Description
189
ETH_1_TXO+
I
Analog
100BASE-TX: Transmit + (Auto MDIX: Receive +)
187
ETH_1_TXO-
I
Analog
100BASE-TX: Transmit - (Auto MDIX: Receive -)
195
ETH_1_RXI+
O
Analog
100BASE-TX: Receive + (Auto MDIX: Transmit +)
193
ETH_1_RXI-
O
Analog
100BASE-TX: Receive - (Auto MDIX: Transmit -)
191
AGND_LAN
Ethernet ground, on some modules connected to common GND
183
ETH_1_LINK_AKT
O
CMOS
3.3V
LED indication output for link activity on the Ethernet port
185
ETH_1_SPEED100
O
CMOS
3.3V
LED indication output for 100Mbit/s
Table 3: Ethernet Signals
2.2.2 Reference Schematics
Ethernet connectors with integrated magnetics are preferable. If a design with external magnetics
is chosen, additional care must be taken to route the signals between the magnetics and Ethernet
connector.
The LED output signals ETH_1_LINK_AKT and ETH_1_SPEED100 can be connected directly to the
LED of the Ethernet jack with suitable serial resistors. There is no need for additional buffering if
the current drawn does not exceeds 10mA.
The Fast Ethernet interface uses the ETH_1_TXO as transmitting lanes and the ETH_1_RXI as
receiving lane. If the Ethernet PHY features Auto-MDIX, the signal lanes RX and TX could be
swapped. We strongly recommend not swapping the RX and TX lanes to keep the compatibility with
all Colibri modules.
The required center tap circuit depends on the supported modules. Currently, the Ethernet
controller on the PXA270 module is the only one that requires a different center tap circuit since it
does not support Auto-MDIX. All the other currently available modules feature a current control
PHY that requires a 3.3V supply at the center tap of the RX and TX lanes. Since all the Ethernet PHY
manufacturers are tending to change from current mode to voltage mode, which requires leaving
the center tab pins of the magnetics unconnected, we recommend adding additional 0R resistors
into the center tab lines. This ensures that the carrier board design is ready for any future Colibri
module with voltage-mode PHY.
The magnetics provide a certain ESD protection which is sufficient for many designs. However,
especially in Power over Ethernet (PoE) systems, additional transient voltage suppressor diodes
(TVS) are highly recommended between the module and the magnetics. More information can be
found in the following application note from Microchip:
http://ww1.microchip.com/downloads/en/AppNotes/00002157B.pdf