where: No. registers = number of Modbus register to be read, starting from the Address 1°
register;
No. bytes = number of data bytes to follow;
Val.reg.1 = register contents beginning from the first.
The Response contains the number of records changed starting from the Address 1° register.
COMMUNICATION ERROR MANAGEMENT
The communication strings are controlled by CRC (Cyclical Redundancy Check). In case
of a communication error the slave will not respond with any string. The master must allow
for a time-out before response reception. If no response is received it infers that a
communication error has occurred.
In the event of a string received correctly but not executable, the slave responds with an
EXCEPTIONAL RESPONSE. The "FUNCTION" field is transmitted with the msb at 1.
EXCEPTIONAL RESPONSE
Address Function Code 2bytes
A Funct + 0x80 CRC
CODE DESCRIPTION
1
ILLEGAL FUNCTION (Function not valid or not supported)
2
ILLEGAL DATA ADDRESS
(The specified data address is not available)
3
ILLEGAL DATA VALUE (The data received have no valid value)
4
CRC Error
82
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