Descripción - Spirax Sarco VLM20 Instrucciones De Instalación Y Mantenimiento

5.6.4 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, as follows:
Exception Code
01
02
03
If the first byte of a message is not equal to the unit's Modbus address, 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.
5.6.5 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.
Device address
8 bits, 1... 247
5.6.6 Normal response message format
Device address
8 bits, 1... 247
5.6.7 Exception response message format
Device address
8 bits, 1... 247
96
Descripción
Invalid function code — function code not supported by device
Invalid data address — address defined by the start address and number
of registers is out of range
Invalid data value — number of registers = 0 or >125 or incorrect data
with the Write Single Coil command
Function Start address
code
8 bits 16 bits, 0... 9998
Function Byte count
code
8 bits 8 bits
Function
code
8 bits
N = Number of registers
16 bits, 1 ... 125
Data
(N) 16-bit registers
Exception code
8 bits
IM-P339-06 MI Issue 2
CRC
16 bits
CRC
16 bits
CRC
16 bits