We have a PCIX board (with MIPS CPU) from some vendor and it has an RJ-45 jack on the board-side, where the cable has an RS-232 plug on the other side. The expected protocol is clearly the same as when using a nullmodem cable between two machines.Now I am wondering whether there is some Linux or *nix flavor that allows me to substitute the cable for a standard patch cable with RJ-45 connectors on both ends (not crossed for obvious reasons)? I read that someone suggested socat for some similar use-case, but it appears that the use case is so arcane that documentation is virtually non-existent on the topic. Of course it's well possible that I simply used the wrong search terms so far.Reasoning: it's almost hard to come by devices that have a COM port nowadays, but most have an ethernet port. Also, the board is in a rather inaccessible location, so to connect to it we've been using mobile devices. And then it's even harder to find machines with COM ports.NB: I'm aware of RS-232 to USB devices, but would prefer a solution as pointed out as it seems more universal.
RJ-45  RS-232, can I substitute the RS-232 side and abuse my Ethernet port as COM port?
tty;ethernet;serial port
It's not clear exactly what you want. If you want to use your existing Ethernet port, that won't be an option for many reasons; the most fundamental being that Ethernet requires precise termination and voltage levels, the hardware on the interface (the PHY) is made to deal with that. Ethernet uses strictly +/- 0.85V and 50ohm termination impedance; RS-232 uses at a minimum +/- 3V, and could be as high as +/-25V, typically +/-12V. I imagine if you did try to connect your Ethernet port to an RS-232 line, it would fry your network interface.Socat is a whole other level, and definitely is not useful here: it's a TCP/IP communication tool: it doesn't know anything about the electrical characteristics of the underlying hardware - it could talk over an RS232 line, but it'll be talking TCP, and you'd need to talk TCP on the other side for it to work.Now, if what you're doing is designing a board, you could put an RJ45 jack with traces to a serial I/O port, which is exactly what the makers of your PCIX board have done. I've also seen Cisco routers like this.The tool you really need is an RS232->USB converter.