Serial port on unused Ethernet pins

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[edit] Introduction

Some routers do not have enough space on the back for a standard RS-232 port and/or you do not want to drill holes in the case. This page explains how to add a serial interface to a non-Gigabit Ethernet port without losing its Ethernet functionality. Image:RT-N12 serial board.jpg


[edit] Notes

This mod will not work on Gigabit ports because Gigabit uses all 4 pairs in the Ethernet cable. In routers where the Ethernet coupling circuits are integrated into the connectors, it would be necessary to tap directly into the pins. In any case, the pins must be disconnected from existing circuits.

[edit] Schematic

Image:RT-N12_serial_schematic.png The TX, RX, and DTR are from the router perspective. They connect to RX, TX, and DSR/CD on the PC serial port. Make a custom cable or adapter to connect the RJ-45 to the serial port.

Any RS-232 level converter circuit can be used as long as the outputs can withstand a short circuit to ground for an unlimited amount of time.