Ethernet Port Lines
ATTENTION! There are two different Ethernet magnetics arrangements: one for original EM1000-...- 00, another one — for the EM1000-...- 01.
Ethernet port of the EM1000 is of 100BaseT type. Onboard electronics of the EM1000 do not include Ethernet magnetics, so magnetics circuitry must be connected externally to pins TX+, TX-, RX+, RX-, and AVCC. The AVCC pin outputs clean power for the magnetics circuitry, which is very sensitive to noise. The voltage on the AVCC depends on the EM1000 version: 3.3V for EM1000-...- 00, 2.5V for the EM1000-...- 01. Separate AGND analog ground pins have been added on the EM1000-...- 01. For the EM1000-...- 00 there is no separate analog ground. Please, note the following:
- The AVCC is an output!
- Do not combine AVCC with the VCC (main power) pin. On the EM1000-...- 00 this is counter-productive, and on the EM1000-...- 01 this will apply wrong voltage to the AVCC pin. Doing so appears to be causing no immediate permanent damage to the EM1000-...- 01, 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 are two connection diagrams based on the YCL-PTC1111-01G — one for the EM1000-...- 00, another one - for the EM1000-...- 01.
Once again, the EM1000-...- 00 is a legacy part that has been replaced with the EM1000-...- 01. In case you have already made the PCB based on the EM1000-...- 00 specifications and are not willing to change it, you can easily modify it to accommodate the EM1000-...- 01 (see diagram below):
- Do not install four 50 Ohm resistors (they are crossed out on the diagram).
- Connect a wire between pins 4 and 7 of the RJ45 connector (pin numbers are for YCL-PTC1111-01G).
- If possible, find a way to install a 220uF capacitor. The circuit will still work even if you don't have this capacitor but you may have FCC/CE certification issues.
- Notice that one of the 0.1 capacitors becomes redundant but that's OK.
- All of the above is based on the assumption that your host PCB was designed correctly and the AVCC output of the EM1000 is not joined together with the main VCC line. If you erroneously had AVCC and VCC combined together then you will need to separate them as well: pin AVCC outputs 2.5V on the EM1000-...- 01 and this is different from the main power on the VCC pin, which is 3.3V. Applying 3.3V to pin AVCC of the EM1000-...- 01 appears to be causing no immediate permanent damage to the device, but the circuit will not work and the effects of prolonged over-voltage on the AVCC line are not known.
It is important to make the PCB wire connections between the Ethernet port pins of the EM1000 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).
The EM1000 also has two Ethernet status LED control lines- see here for details.