![]() ![]() This may be because the function code is only applicable to newer devices, and was not implemented in the unit selected. The function code received in the query is not an allowable action for the server (or slave). This number tells the slave which table to access and whether to read from or write to the table. The second byte sent by the Master is the Function code. The error-checking field of a message frame contains a 16-bit value (two 8-bit bytes) that contains the result of a Cyclical Redundancy Check (CRC) calculation performed on the message contents. ![]() RTU Mode message frames include an error checking method that is based on a Cyclical Redundancy Check (CRC). This field contains two ASCII characters that represent the result of a longitudinal redundancy calculation for all the fields except the starting colon character and ending CR LF pair of characters. LRC Longitudinal Redundancy Check (ASCII Mode Only) In the ASCII transmission mode, the character frame includes an LRC field as the last field preceding the CRLF characters. The parity bit will then be set to a 0 or a 1, to result in an even (even parity), or odd (odd parity) total number of 1 bits. Each character in RTU mode contains 8 bits. If even or odd parity checking is selected, the number of 1 bit in the data portion of each character frame is counted. This determines how the parity bit of the character's data frame is set.
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