I am using the BF537 with the SMSC LAN8700 Ethernet PHI. My PCBs have been working in the field, but I noticed that I left off the pull-up resistor on the MDIO line. Most of my boards work, but a few fail a basic Ethernet PHI loopback test. How can the circuit work at all if the pullup is missing? Does the the BF537 have an internal pullup?