Communication - LEGRAND RS485 Manual Del Usuario

146 71

cOmmunicatiOn

The JBUS/MODBUS
involves a dialogue using a master-slave hierarchical
structure. There are two possible dialogues:
• the master communicates with a slave (146 68 product)
and waits for its reply
• the master communicates with all the slaves (146 68
product) without waiting for their reply.
tHe standard cOmmunicatiOns frame
The standard communications frame consists of:
Slave address
According to the JBUS/MODBUS
sion time must be less than 3 silences, i.e. the emission
time of 3 characters so that the message is processed
by the 146 68 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)
146 71 - Ref.: N951/00

used by the 146 68 product
®
Function code
protocol, transmis-
®
The mode of communication is the RTU (Remote
Terminal Unit) using hexadecimal characters of at least
8 bits.
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 instruments present on the network (only for
functions 6 and 16)
Comment:
The response time (time out question/answer) is 250 ms
maximum .
CRC 16