Longitudinal Redundancy Check for Modbus

Longitudinal Redundancy Check (LRC) for Modbus PLC Controllers using ASCII
LRC.m - The value appended to the end of each communication to assure that the data received is not corrupted. The LRC is the 2's compliment negation of the sum. When the total adition in the LRC constitutes a number greater then 8bits only the lowest 8bits are used to compute the LRC. LRC.m has two modes, in mode 1 it compares the LRC received to one calculated and in mode 2 it calculates an LRC and appends it onto a string for outgoing communication.