rbias
Thanks.
I read the silicon rev from the chip (using UART for debugging) and found it to be Rev. B4, so Rbias=2k7. I still have the link problem.
Reading on the Rev. B4 Silicon Errata I learned the chip has quite many bugs ranging from incorrect LED illumination to bad reception when the TPIN+/TPIN- are inverted, it's necessary to run the SPI at >8MHz...
I run the AVR uC at 12.5MHz, from the CLKOUT of ENC28J60, and the SPI is used at 6.25MHz. I think this is Ok, because it's recommended in the Errata and the uC can communicate with ENC28J60.
If you used a Rev. B4 chip, please share your experience.