Versatile control system PLC87(A) part 1:

In the industry, there is no such thing as process automation without Programmable Logic Controls (PLCs). These systems are typically quicker and easier to program than just about any microcontroller circuit, and they also allow variables to be observed during program execution. The PLC87 and 87A boards described here are basically 8751 (or 87C550) based systems capable of executing Simatic-S5 oriented command sequences, the S5 command set representing a well-established industry standard.