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PanaFlow™ MV80, MV82 & MV84 User’s Manual 113
Chapter 4. Serial Communications
4.2.6.10 Error Responses
If an error is detected in the message received by the unit, the function code in the response is the received function
code with the most significant bit set, and the data field will contain the exception code byte (see
Table 12 below).
Table 12: Exception Codes
Exception Code Description
01 Invalid function code - function code not supported by device.
02 Invalid data address - address defined by the start address and
number of registers is out of range.
03 Invalid data value - number of registers = 0 or >125,
or incorrect data with the Write Single Coil command.
If the first byte of a message is not equal to the unit's Modbus address or if the unit detects a parity error in any
character in the received message (with even or odd parity enabled) or if the message CRC is incorrect, the unit will
not respond.
4.2.6.11 Command Message Format
The start address is equal to the desired first register number minus one. The addresses derived from the start
address and the number of registers must all be mapped to valid defined registers, or an invalid data address
exception will occur.
Table 13: Address Register Mapping
Device Address Function Code Start Address N = No. of Registers CRC
8 bits, 1...247 8 bits 16 bits, 0...9998 16 bits, 1...125 16 bits
4.2.6.12 Normal Response Message Format
Table 14: Normal Response Message Format
Device Address Function Code Byte Count = 2 x N Data CRC
8 bits, 1...247 8 bits 8 bits (N) 16-bit registers 16 bits
4.2.6.13 Exception Response Message Format
Table 15: Exception Response Message Format
Device Address Function Code + 0x80 Exception Code CRC
8 bits, 1...247 8 bits 8 bits 16 bits