User`s manual

88 RabbitCore RCM3400
B.4.4.3 Ethernet Port
Figure B-10 shows the pinout for the Ethernet port (header J7). Note that there are two stan-
dards for numbering the pins on this connector—the convention used here, and numbering
in reverse to that shown. Regardless of the numbering convention followed, the pin posi-
tions relative to the spring tab position (located at the bottom of the RJ-45 jack in
Figure B-10) are always absolute, and the RJ-45 connector will work properly with off-
the-shelf Ethernet cables.
Figure B-10. RJ-45 Ethernet Port Pinout
RJ-45 pinouts are sometimes numbered opposite to the way shown in Figure B-10.
Two LEDs are placed next to the RJ-45 Ethernet jack, one to indicate a live Ethernet link
(LNK) and one to indicate Ethernet activity (ACT).
The transformer/connector assembly ground is connected to the RCM3400 Prototyping
Board printed circuit board digital ground via a 0  resistor “jumper,” R46, as shown in
Figure B-11.
Figure B-11. Isolation Resistor R46
The factory default is for the 0  resistor “jumper” at R46 to be installed. In high-noise
environments, remove R46 and ground the transformer/connector assembly directly to
ground by soldering a wire between the RJ-45 transformer/connector assembly and
ground. This will be especially helpful to minimize ESD and/or EMI problems.
ETHERNET
RJ-45 Plug
1. E_Tx+
2. E_Tx
3. E_Rx+
6. E_Rx
1
8
RJ-45 Jack
RJ-45 Ethernet Plug
R46
Chassis
Ground
Board
Ground