Pavone Systems MC 315 Series, Technical Manual

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MODBUS RTU PROTOCOL
The addresses in the table below follow the standard routing specified in the reference guide of the
Modicom PI-MBUS-300. An abstract is provided below to ensure smooth user-unit communication.
“All data addresses in Modbus messages are referenced to zero. The first occurrence of a data item
is addressed as item number zero. For example:
The coil known as ‘coil 1’ in a programmable controller is addressed as coil 0000 in the data
address field of a Modbus message.
Coil 127 decimal is addressed as coil 007E hex (126 decimal).
Holding register 40001 is addressed as register 0000 in the data address field of the message. The
function code field already specifies a ‘holding register’ operation. Therefore the ‘4XXXX’ reference
is implicit.”
Execute the MAKE – BACKUP function to confirm a new value entry in E2prom. If such function is not
executed, the value prior to the change is restored when the MC 315 is switched off.
Unless otherwise specified, numeric values (such as addresses, codes, and data) are expressed as
decimal values.
The MODBUS RTU Il protocol is only available on COM2 RS485.
COMMUNICATION ERROR MANAGEMENT
Communication strings are controlled via CRC (Cyclical Redundancy Check). In case of communication
error, the slave does not reply with a string. The master should consider a timeout for response receipt.
If no response is received, the master should assume that a communication error has occurred.
MANAGEMENT OF ERRORS IN THE DATA RECEIVED
If a string is duly received but is not executable, the slave replies with an EXCEPTION RESPONSE
according to the following table.
CODE DESCRIPTION
1 ILLEGAL FUNCTION (The function is invalid or not supported)
2 ILLEGAL DATA ADDRESS (The specified data address is no longer available)
3 ILLEGAL DATA VALUE (The received data has an invalid value)
SUPPORTED FUNCTIONS:
FUNCTION DESCRIZIONE
01 READ COIL STATUS (Logical output status reading)
02 READ INPUT STATUS (Logical input status reading)
03 READ HOLDING REGISTERS (Programmable register reading)
04 READ INPUT REGISTERS (“Read-only” register reading)
05 FORCE SINGLE COIL (Single output status writing)
06 PRESET SINGLE REGISTER (Writing of a pre-set register)
15 FORCE MULTIPLE COILS (Multiple output writing)
16 PRESET MULTIPLE REGISTERS (Multiple register writing)
Funct + 80h EXCEPTION RESPONSE