SPRUI97E May 2017 – September 2025 AM5716 , AM5718
The PHY address LSB for U9 and U15 gets determined by the signal level at the PHY's COL pin during reset release. The PHY has a pull-down resistor connected to this pin to enable latching the value of 0. Unfortunately, this pin is also connected to one of the RJ-45 connector LEDs that pulls the signal to an undefined voltage of about 1.4V during the reset time. Therefore, the PHY address can incorrectly latch a value of 1. The LED circuit should be configured for active-high indication and the connections to the LED reversed with the cathode connected to ground. This allows the LSB of the address to be properly latched. Please refer to Section 6 of the TLK1XX Design and Layout Guide Application Report (SLVA531) for more information. The current software workaround programs the RXLINK pin with a pull-down resistor and then pulses the PHY reset from a GPIO, to cause it to latch the PHY address correctly.