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The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a fieldbus or computer network that plugs into the PLC. The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control , distributed control systems , and networking .
The output will be high (true) only when all gates are in the high-impedance state, and will be low (false) otherwise, like Boolean AND. When treated as active-low logic, this behaves like Boolean OR, since the output is low (true) when any input is low. See Transistor–transistor logic § Open collector wired logic.
IEC 61131-3 is the third part (of 10) of the international standard IEC 61131 for programmable logic controllers.It was first published in December 1993 [1] by the IEC; the current (third) edition was published in February 2013.
The input modules receive information from sensing instruments in the process (or field) and the output modules transmit instructions to the final control elements, such as control valves. The field inputs and outputs can either be continuously changing analog signals e.g. current loop or 2 state signals that switch either on or off , such as ...
SIMATIC devices have input and output modules to connect with controlled machines. The programs on the SIMATIC devices respond in real time to inputs from sensors on the controlled machines, and send output signals to actuators on the machines that direct their subsequent operation.
The function block diagram (FBD) is a graphical language for programmable logic controller design, [1] that can describe the function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines.
In 1969, Motorola offered the XC157, a mask-programmed gate array with 12 gates and 30 uncommitted input/output pins. [3] In 1970, Texas Instruments developed a mask-programmable IC based on the IBM read-only associative memory or ROAM. This device, the TMS2000, was programmed by altering the metal layer during the production of the IC.
Fan-out is ultimately determined by the maximum source and sink currents of an output and the maximum source and sink currents of the connected inputs; the driving device must be able to supply or sink at its output the sum of the currents needed or provided (depending on whether the output is a logic high or low voltage level) by all of the ...