Ethernet; Signal Description; Design Guideline - Advantech SOM-ETX Series Design Manual

5.8 Ethernet

SOM-ETX supports the IEEE802.11b network interface and flexible dynamically
loadable EEPROM algorithm. The network interface complies with the IEEE standard
for 10BASE-T and 100Base-T, TX and T4 Ethernet interfaces.

5.8.1 Signal Description

Table 5.18 shows SOM-ETX ethernet signals, including pin number, signals, I/0,
power plane, terminal resistors, damping resistors and descriptions.
Table 5.18 Ethernet signals description
Pin Signal
D91 LAN_RXD-
D93 LAN_RXD+
D95 LAN_TXD-
D97 LAN_TXD+
D10 LILED
D12 ACTLED
D14 SPEEDLED

5.8.2 Design Guideline

5.8.2.1 Differential Pairs(TX,RX)
Route the transmit and receive lines on the input (SOM-ETX module) side of the
coupling transformer on the baseboard PCB as differential pairs, with a differential
impedance of 100 Ohms. PCB layout software allows determining the correct trace
width and spacing to achieve this impedance after the PCB stack-up configuration is
known.
The TXD, TXD# signal pair should be well separated from the RXD, RXD# signal
pair. Both pairs should be well separated from any other signals on the PCB. The
total routing length of these pairs from the SOM-ETX module to the Ethernet jack
should be made as short as practical. If the baseboard layout doesn't care where the
Ethernet jack is located, it should be placed close to the SOM-ETX module pins.
Advantech SOM-ETX Design Guide
I/O Description
I Ethernet Receive Differential Pair. These pins receive the
I serial bit stream from the isolation transformer. The bit stream
can be two-level (10BASE-T) or three-level (100BASE-TX)
signals depending on the mode of operation.
O Ethernet Transmit Differential Pair. These pins transmit the
O serial bit stream for transmission on the Unshielded Twisted
Pair (UTP) cable. The current-driven differential driver can be
two-level (10BASE-T) or three-level (100BASE-TX) signals
depending on the mode of operation. These signals interface
directly with an isolation transformer.
O The Link Integrity LED pin indicates link integrity. If the link is
valid in either 10 or 100 Mbps, the LED is on; if link is invalid,
the LED is off.
O The Activity LED pin indicates either transmit or receive
activity. When activity is present, the activity LED is on; when
no activity is present, the activity LED is off.
O The Speed LED pin indicates the speed. The speed LED will
be on at 100 Mbps and off at 10 Mbps. This LED is not
supported by all SOM-ETX boards
Chapter 5 Carrier Board Design Guidelines 89