I always just called it a serial port, because I could never remember DB9 to begin with. I really hope I remember this so I can impress some nerds in the future with how pedantic I can be. (I don't know how to write that last sentence without it sounding sarcastic, but I really meant it.)
Some other pedant might come along if you keep just calling it a serial port. They might mention that it’s specifically RS-232, and that DB-25 is also used for that. They might also mention that “serial port” could include ports for RS-422 and RS-485. They might even mention SIO and USB.
Null modem, crossover, DTE, DCE, straight-through, full handshaking, no handshaking, RS-232 or TTL levels. Plus CAN, RS-485, RS-422, CGA video, RGB video, and any number of industrial things use or can use the same DE9 connector (including sometimes for power).
DEC equipment had something similar. A 6 pin "MMJ" connector. It almost looks like RJ45 except the clip was off center.
I also remember some 90's terminal servers that had enormous "octopus" cables. There was a single connector on the box that broke out to 8 to 16-ish DB25 serial ports.
Are you sure those weren't using RS-232 over TCP/IP over Ethernet?
That is quite common in the pro audio/video installation world, where RS-232 is common but needs extenders for longer distances.
Within A/V, the norm for local RS-232 lines is actually not DE9 but 3-pin terminal blocks! (RX/TX/GND)
I've seen those even on Cisco video codecs, priced $10'000+.
No, most Cisco devices has an RJ45 shaped RS232C port that needs a special cable to do anything with. It's proprietary, but there's one in every networking guy's backpacks so the situation is only as bad as Lightning cable for iPhone. Most(but not all!!) networking gears that compete with Cisco uses the same cable as well.
Eh, depends on "proprietary", I guess. In the PLC world, using an RJ45 for a variety of serial uses is not uncommon. I've never touched a Cisco router in my life, but I've got a few things like these laying around:
Those are some interesting connectors since they have a REAL RJ45 socket. Also interesting that they come prewired and not some assembly required like the ones from amazon do.
The pinout is also called a Yost Cable. You can read about it on https://yost.com/computers/RJ45-serial/ but its an interesting solution to converting DTE and DCE sides to using a standard port and cable. The downside is that the DIY adapters online need some soldiering to bridge the ground wires and more.
I do believe the DTE and DCE pinouts on the yost page are swapped though. I recently tested the pinouts of a Cisco DE-9 to 8P8C (DB-9 to RJ45) with a multimeter and came up with the DCE pinout instead of the DTE one. I then built an adapter with the DCE pinout to connect to my servers serial port and use them as a make shift null modem cable for terminal access.
If I would have know more about this 5 years ago while still at a previous employer, there was some old equipment that used an unknown pinout that would have gotten a DB-9 to RJ45 adapter slapped on it to change it to Cisco/Yost pinout. I was told not to loose the serial cable in the rack with the device because it was the only one that worked on it but never investigated more into it to find out if it was a straight through, null modem, or something else entirely.
I've got a "Sentry Commander" remote power switch and serial server, with four 6P6C connectors for its serial ports to hook to machines and two 8P8C connectors for its own serial console and modem port. I'm sure it shipped with its own proprietary cables long since lost, but I just use RJ12 cables and those "RJ45"->DE9 modular adapters.
The thing I don't get about this is why did people think it was a good idea to have a serial connection over DB-25? You honestly need only 3 wires. Not 25
For a Parallel port, sure 25 wires is right there. But not for a serial port
Plus the differential versions of most of those signals for long distance doubles the number of pins. And they have optional synchronous clocks. I did some WAN work for 3Com back in the day... :)
