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controllers had to be easily The development of the PLCs was programmable by plant engineers or maintenance personnel. originally directed by the in the 70s the PLCs already requirements of the automakers. incorporated the microprocessor. These constantly changed the control systems in their production In 1973, PLCs with the communication capability - lines so that they needed a more Modbus of MODICON appeared. In economical way to do it since, in this way, the PLCs were able to the past, this required extensive exchange information between re-wiring of relay banks. Thus, in them and could be located far the late 1960s, the industry from the processors and the increasingly needed a robust, objects they were going to control. flexible and easily modifiable economic control system. Thus, in In the mid-1970s - PLC technology appeared, based on bit-slice 1968 the first programmable microprocessors (eg AMD automatons (APIs or PLCs) appeared. The American company 2901/2903). The main producers Bedford Associates thus suggested of PLCs at that time became companies such as: Allen-Bradley, a Digital Modular Controller Siemens, Festo, Fanuc, Honeywell, (MODICON) for use in an Philips, Telemecanique, General automotive company and Electric etc. Thus, for each MODICON 084 was the first PLC microprocessor model, there was a with an industrial application PLC model based on it, although (1968). The new the 2903 was one of the most used. Historical Background: