* To avoid damage to the Synergy unit or to the RS485 master, do not connect to this pin
TRANSMISSION MODES
ASCII and RTU transmission modes are defined in the Modbus protocol specification. Synergy uses only the RTU mode for the
telegram transmission.
TELEGRAM STRUCTURE FOR RTU MODE
The Modbus RTU structure uses a master-slave system for message exchange. In the case of the Synergy system, it allows up to
32 slaves, and one master. Every telegram begins with the master making a request to a slave, which responds to the master in a
defined structure. In both telegrams (request and answer), the used structure is the same: Address, Function Code, Data and
CRC.
Master (request telegram):
Address
(1 byte)
Function
(1 byte)
Request Data
(n bytes)
CRC
(2 bytes)
Slave (response telegram):
Address
(1 byte)
Function
(1 byte)
Response Data
(n bytes)
CRC
(2 bytes)
Address
The master initiates the communication sending a byte with the address of the destination slave. When responding, the slave also
initiates the telegram with its own address. Broadcast to address 0 (zero), is not supported
Function Code
This field also contains a single byte, where the master specifies the kind of service or function requested to the slave (reading,
writing, etc.). According to the protocol, each function is used to access a specific type of data. For the available list of supported
functions, refer to Section 2.
MAN-SGY-012-V11 EC 5195
Fairford Electronics Ltd - Synergy Modbus RTU Programming Manual - 22nd February 2016
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