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The PFBOUT pin is a regulated 1.8V supply generated inside the device from the 3.3V supply. The device will not operate correctly if the PFBIN pins do not receive this 1.8V supply.
3.Probe the RBIAS pin
The voltage should be ~1.2V. The RBIAS pin sets the main reference bias for the device. If the voltage or current for this pin is not correct, it could affect the entire device.
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Power down the board and verify key resistances
1.Resistance to ground across the RBIAS resistor should be 4.87 kOhms+/- 1%
2.Resistance across the transmit and receive terminations should be 50 Ohms +/- 1%
3.Resistance across the MDIO pull-up resistor should be approximately 1.5 kOhms
Problems can occur when a very small (10's of Ohms) pull-up resistor is used.
Power up the board and verify key signals
1.Probe the RESET_N signal
The reset input is active low and is connected to a 10 kOhm pull down resistor. It is important to confirm that the controller is not driving the RESET_N signal low. Otherwise, the device will be held in reset and will not respond.
2.Probe the X1 clock
Verify the frequency and signal integrity. For link integrity the clock needs to be within +/- 50ppm of the default (25MHz for MII / 50MHz for RMII).
3.Probe the TD+/- transmit signals
Measure the transmit voltages using a
100 Ohm terminated Pig-tail cable
4.Probe strap pins during initialization.
In some cases, other devices on the board (e.g. MAC) will pull or drive these pins unexpectedly.
