Programmable Logic Controllers - Assignment Example

In contemporary society, electronic devices are used in a variety of ways. Electronic devices which make use of microprocessors rely on signals to understand information. Signals are available in two forms, i.e. Digital and analog. Electronic devices can only understand information that is in digital format, and hence the analog signals are meaningless in such devices. For this reason, the conversion of analog to digital signals is essential, especially considering that most real-life situations lead to the production of analog signals. The analog-to-digital conversion of information, changes the format of the information, without altering its content. Microprocessors are used for the conversion of the analog signal to digital.

The principle used in the conversion of analog signals to digital signals by the microprocessor is voltage variation. The microprocessor used sensors, which detect the incoming analog signals and translate them into voltage levels. For instance, the translation of temperature of 0 – 1000c, leads to the assignment of 0 volts to 00c, and 5volts to 1000c. Any value that is above 0volts represents a HIGH, and hence microprocessor can show the actual value, depending upon the number of levels the microprocessor can represent.

The resolution of the A/D converter refers to the number of intervals that can be divided from a certain analog input range. Since the interpretation of the analog input (e.g. temperature) requires assigning voltage levels, the number of levels which can be represented is determined by the resolution. The resolution of the A/D converter is represented in bits, for instance, an n-bit A/D converter has a resolution of 1/2n. The word length, as used in the microprocessors refers to the number of intervals or levels which can be divided from a certain analog signal.

Major functions:
ADD – this function is used in PLC, to add two numerical values. It is used, for instance, to add a numerical value from source A, to another numerical value from source B. the result of the function is usually placed in the destination register.
SUB – when this instruction is used in PLC, it does the opposite of the ADD instruction. It subtracts a numerical value a, from source A, from another numerical value b, from source B. the result of the function is then stored in the destination register.
MUL – this instruction is used for multiplication purposes. When the instruction is used, two numerical values from sources A and B are multiplied, and the result is stored in the destination register.
DIV - this instruction is used to divide two numerical values, from sources A and B, and the result is stored in the destination register.
ZRST – Zone reset. It is used to move data from its location to a new destination.
CMP – this instruction compares arithmetic operations specified in an expression.

Registers provide temporal memory. They are used to temporarily hold instructions or data. For instance, the registers can hold data that is being fetched or written to memory. They help is speeding up the processor, as it doesn’t need to read the instructions from the main memory, whenever it requires them.