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We developed an Ethernet-connected device that uses the Microchip PIC18F97J60 controller. This particular PIC contains the PHY that allows us to simply connect the chip to Ethernet magnetics and then to the outside world.

An added complication is that this device is PoE powered.

Our customer now wants us to provide a pass-through port that allows multiple units to be daisy-chained without them (the customer) needing to install an Ethernet switch.

The data rate is quite slow - significantly-less than 10 Mbps.

Obviously, we now need to integrate an Ethernet switch within our device. Been searching for simple options and one that bubbled to the top is the Micrel KSX8863 family. This is a 3-port switch that has two PHY interfaces built-in as well as a Mii port. The thought was that we might be able to connect that mii port directly to the PIC controller.

Unfortunately, what I know about Ethernet hardware would fit on the head of a very tiny pin. Consider me to be a complete newbie in this regard.

However, I suspect that because our PIC controller already has the PHY built-in and does not appear to provide direct access to the mii port inside the PIC, a direct connection between the PIC's PHY and the KSZ chip's mii port is not possible.

I'm asking for clarification on this: do I need to be looking for either a different PIC controller (that does not include the PHY) or a different Ethernet Switch that has three PHY ports?

Or: is there some way that I can indeed directly connect the PIC18F97J60 to the mii port on the KSZ8863 Ethernet Switch?

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  • \$\begingroup\$ Yes, you'll need a different switch. \$\endgroup\$ – immibis May 23 at 5:23
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You don't necessarily need a switch. If there are no many devices on your network and the amount of data is small, the hub might be enough. You would need to handle collisions in software e.g. by resending the data after random delay.

Here's an example of a simple hub: http://www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htm. You did not mention the PoE mode you are using, but with this solution, mode B (power on non-data pairs) is easy to implement.

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