What is the PLC taking the opposite value command? -Solutions - Huaqiang Electronic Network

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What is the opposite value command in PLC programming? For example, after performing a real number operation, you might want to get the opposite value—like turning 2.0e+01 into -2.0e+01. Is there a direct command for this? While multiplying by -1 is a common workaround, I'm specifically looking for a built-in instruction that can achieve this more efficiently. The opposite value of a real number involves flipping the sign bit of the mantissa. This is typically done by negating the value, which changes the sign without altering the magnitude. In PLCs, especially those using IEEE 32-bit floating-point numbers, there's often a specific instruction designed for this purpose. One such instruction is NEGR, which is used to negate a 32-bit IEEE floating-point number. This command works directly on the accumulator and flips the sign bit (bit 31) of the number stored there. The result is then saved back to the same location or transferred elsewhere as needed. Here’s how it works: - Load the real number into the accumulator using a command like LID8. - Apply the NEGR instruction to invert the sign of the floating-point number. - Transfer the result from the accumulator to a memory address using a command like TMD10. Example:
LID8 // loads the value into accumulator 1 (e.g., ID8 = 1.5E+02)
NEGR // negates the 32-bit IEEE floating-point number in accumulator 1
TMD10 // stores the result in MD10 (e.g., MD10 = -1.5E+02) Using NEGR is an efficient way to handle sign inversion in real-number operations, ensuring accurate and fast execution in control systems.