Communication workhorses in the industry have been around since the always-underestimated, industrious Neanderthals first used serial and parallel communications to wire up their caves for monitoring fire wood inventories and controlling cave fire pits while the Ice Age raged outside.
Take the venerable RS-232, for example. RS-232 was established as a standard for low-speed serial connection of computers to peripherals. The standard has been renamed many times over the years and evolved into RS-422 and TIA-485-A (RS-485), all serial standards. USB came in and usurped RS-232 for connecting devices to computers. But, it turns out, there are still times where a serial connection like RS-232 and friends come in handy.
First, the problems with USB as compared with simpler serial data/control communications. USB requires a computer on one end because USB has a master/slave relationship. It requires drivers. It's not suitable for control purposes. There are no slave/slave connections with USB.
It so happens, RS-232 and its serial cousins RS-422 and TIA-485-A are alive and well in applications where simpler, dependable, reliable, hard-wired communications are required. They see action in AV (audio/video) gear, low-speed communications in commercial aircraft, industrial control systems, theatre and performance venues, home/building automation, and even model railways. There are advantages to a tried-and-true simple approach.
Back in the day, the parallel port also connected computers to peripherals. Known also as a parallel communication physical interface, a printer port or Centronics port, it was standardized as IEEE 1284 in the late 1990s. IEEE 1284 defines bidirectional implementation. Faster than a serial connection like RS-232, parallel connections were the mainstay for printers and scanners in ancient times. USB, Ethernet, and WiFi have replaced the parallel port for such devices. However, there's still a place for a fast, simple connection. Multi-purpose printers still ship today with a parallel port. CNC milling machines sport parallel ports. The parallel port is the easiest way to get connected to an external circuit board since there is no need for serial-to-parallel conversion. Parallel port control of robots is an ongoing thing. And industrial automation takes advantage of the parallel standard.
Serial and parallel communication standards are well-documented and have a predictable outcome and long-running, proven history. Mouser is chock-full of related hardware and semiconductors. [1] [2] [3] Other approaches can be used but, aside from the implementation part, there is one huge aspect where "old is new" again, and that's security.
When devices are hard-wired and connected with simple protocols, the possibility of intrusion and exploit is reduced. Massively reduced. USB, and across intra- or internet (wireless or wired), all require drivers and additional gear. In the case of the simpler serial and parallel communications, MITM (Man In the Middle) means someone has cut into the actual wiring which is something visible, easily understood, and obvious as compared the huge, nebulous attack surface of the internet (wired or wireless), and the vagaries of USB.
USB is more exploitable than the simpler connections of parallel and serial ports since USB is "smarter" and more complex, which translates to more vulnerable and more attack vectors. Whether used for communication or storage, every USB implementation has a controller chip with firmware. That's the beginning of the attack surface. Just do a search in your favorite search engine with the words "USB" and "exploit" for the latest horror stories.
(By the way, this blog is chock full of useful key words for searching about the world of parallel and serial ports and wiring; feel free to use the words early and often.)
Whether one is launching into robotics, home automation, AV, or industrial control projects, it's worth it to think about design goals in terms of security, in terms of solid data and control code transfer using the well-established, highly documented serial and parallel options.
Especially if controlling a blazing fire place in your favorite cave.
[1] https://www.mouser.com/Search/Refine.aspx?Keyword=%22RS-232%22
[2] https://www.mouser.com/Search/Refine.aspx?Keyword=%22RS-485%22
[3] https://www.mouser.com/Search/Refine.aspx?Keyword=%22IEEE+1284%22