Nano Ethernet Shield
There are at least 3 versions of the Nano Ethernet shield in shops. Black version is by Robotdyn, red and blue version are from different manufacturers. The shields use a schematic based on the schematics recommended in the datasheet for a 5 V MCU. They use logic gates (74HCT08) instead of a Tri-State Digital Buffer (74HC125) to convert the MISO line to 5 V. This creates problems. SPI device not selected by CS pin should release the MISO line by setting the output pin to HI-Z state. The enc28j60 of course does this, but the logic gate can't. It stays HIGH, blocking the bus. No other device can be used on SPI with this shield attached. (Many 5 V SD card adapters have the same problem with then level conversion on the MISO line.)
The new 3.3 V Nano boards could be damaged by this shield, while without the 5 V conversion the shield would be OK for a 3.3 V Nano. This applies to any 3.3 V MCU with this shield wired as module.
The shields can be converted to work with a 3.3 V Nano.
To remove the interfering and unnecessary conversion to 5 V, remove the 74HCT08 chip from the shield and connect the contact with a trace to pin 12 to the contact to enc28j60 MISO pin. The 74HCT08 has 4 logical AND channels. The shield uses two of them as buffers by tying both inputs together (1 and 1 is 1, 0 and 0 is 0).
If you want to use the INT pin (EthernetENC doesn't use it), then connect the contact with the trace to pin 2 to the inputs of the channel. You can determine the right contact by following the trace or by measuring the continuity with a multimeter.
Some shields have a 5V pull-up on CS and RESET pins. The shield by Robotdyn doesn't have this problem.
Modification of the Robotdyn version for a 3.3 V board:
Modification of the red version to avoid the MISO line problem:
Modification for the pull-up resistors from 5 V to 3.3 V on the red version:
