Programmable Logic Controller Communicates RS-232  By Eugene Kowch, P.I.D. Consultants Inc. PLC's have communication ports that can be configured to talk all kinds of protocols. One of the most useful in home systems is the ASCII In/Out non-sequence protocol.

System integration is becoming an important issue in the home automation scene. New homes have a number of systems: security, heating, lighting, drapery, audio, video, etc. Each system has its own controller and takes care of its own I/O (Inputs and Outputs). At present, the homeowner needs to learn how each system works and remember the different operational commands to control their electrical environment. This process can be simplified with the integration of a Programmable Logic Controller (PLC).

Most home systems are coming out with an RS232 communication interfaces, which enables two systems to talk to each other. PLC's have communication ports that can be configured to talk all kinds of protocols. One of the most useful in home systems is the ASCII In/Out non-sequence protocol.

Each home system has their own unique command set of ASCII codes available for monitoring and operating their respective system. The PLC can read and write these codes and translate them to one common user interface, like a touch panel. The touch panel is typically setup as a graphic interface with buttons for each subsystem, thus giving the homeowner one overall control system to operate. The PLC acts on a supervisory level, communicating to all home systems via RS232 connections and passing info to and from touch panels located throughout the home.