Communication - Bticino Modbus RS485 Mode D'emploi

Communication

The MODBUS® used by the F3N300 product involves a dialogue using a master-slave hierarchical structure. There are
two possible dialogues:
• the master communicates with a slave (F3N300 product) and waits for its reply
• the master communicates with all the slaves (F3N300 product) without waiting for their reply.
The mode of communication is the RTU (Remote Terminal Unit) using hexadecimal characters of at least 8 bits.
The standard communications frame
The standard communications frame consists of:
Slave address
According to the MODBUS® protocol, transmission time
must be less than 3 silences, i.e. the emission time of 3 cha-
racters so that the message is processed by the F3N300
product.
To use this information correctly, it is indispensable that the
functions be used in accordance with the codes:
3: to read n words (maximum 128).
6: to write one word.
8: to diagnose exchanges between the master and the
slave via meters 1, 3, 4, 5 and 6.
10: to write n words (maximum 128).
Communication table
>
The communication tables are available on the CD-Rom supplied with the RS485 MODBUS® module for F3N300 product.
24
Function code Address Data
NB:
1 word <=> 2 octets <=> 16 bits
2 words <=> 4 octets <=> 32 bits
When selecting slave address 0, a message is sent to all the ins-
truments present on the network (only for functions 6 and 16).
Comment:
The response time (time out question/answer) is 250 ms
maximum.
CRC 16