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. All this shields use the same schematics, but Robotdyn has a different PCB layout. The shields 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.

To remove the 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 wake-on-lan function 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.

Modification of the common version:

Modification of the Robotdyn version: