An RS232 connection is this context is most commonly used for connecting to a remote-control system from a company such as Crestron or AMX. Such systems are extremely flexible, but they're really NOT designed to be programmed by the end user - programmers generally need to have quite a bit of training and experience with the particular system.
With these systems, the programmer designs the GUI on the touchpanel or has a button-style remote custom engraved. The remote or touchpanel then communicates with a control processor, which in turn is programmed to operate all of the equipment in the system - using RS232, TCP/IP, IR-remote emulation, contact closures, power relays . . . whatever is best for each individual piece of gear.
It is the program that resides in the control processor that is written with the specific protocol a RS232 controlled device; these protocols are almost completely non-standardized across the industry, so the programmer will either use a pre-written chunk of code provided by the manufacturer, or have to write one from scratch.
With these systems, the programmer designs the GUI on the touchpanel or has a button-style remote custom engraved. The remote or touchpanel then communicates with a control processor, which in turn is programmed to operate all of the equipment in the system - using RS232, TCP/IP, IR-remote emulation, contact closures, power relays . . . whatever is best for each individual piece of gear.
It is the program that resides in the control processor that is written with the specific protocol a RS232 controlled device; these protocols are almost completely non-standardized across the industry, so the programmer will either use a pre-written chunk of code provided by the manufacturer, or have to write one from scratch.