Ethernet Port Lines
Ethernet port of the EM1202 is of 100BaseT type. Onboard electronics of the EM1202 do not include Ethernet magnetics, so magnetic circuitry must be connected externally to pins TX+, TX-, RX+, RX-, and AVCC. The AVCC pin outputs clean 2.5V power for the magnetics circuitry, which is very sensitive to noise. Separate AGND analog ground is also provided. Please, note the following:
- The AVCC is an output!
- Do not combine AVCC with the VCC (main power) pin. This will apply wrong voltage to the AVCC pin. Doing so appears to be causing no immediate permanent damage to the EM1202, but the circuit will not work and the effects of prolonged over-voltage on the AVCC line are not known.
You can use either a standalone magnetics part (such as YCL-PH163112) or RJ45 connector with integrated magnetics (i.e. YCL-PTC1111-01G). Here is a connection diagram for the YCL-PTC1111-01G jack with integrated magnetics.
It is important to make the PCB wire connections between the Ethernet port pins of the EM1202 and external magnetics circuitry as short as possible. Making the wires too long may cause the noise level generated by your PCB to surpass the maximum radiated emission limits stipulated by FCC/CE regulations. Additionally, longer Ethernet lines on the PCB will make your board more susceptible to the damage from the ESD (electrostatic discharge). Follow these three recommendations:
- Route TX+, TX-, RX+, RX- in such a way that they do not cross each other. Try to avoid using vias (keep on the same board side).
- Keep more or less uniform distance between "+" and "-" traces of each pair.
The EM1202 also has two Ethernet status LED control lines- see here for details.