Hitachi SJ Series, User Manual

Page: 498 / 786

14-7
Chapter 14 RS485 Communication
14.3 Message Structure
14.3.1 Queries and responses
• A command message sent from the master to a slave is
called a “query”, and an answering message from a slave
is called “response”.
Query
14.3.2 Slave addresses (communication
station numbers)
• A slave address is a number from 1 to 247 which is set in
each inverter (slave) in advance. (Only the inverter
having the address matching the query’s slave address
will take the query.)
• If you designate “0” to the slave address of transmission
destination in the master inverter, you can activate a
broadcasting to all stations (simultaneous broadcasting).
Under the broadcasting mode, all slaves receive data but
do not return responses.
Transmission formats of queries and responses are as
shown below:
Response
• Under the broadcasting mode, data readout and
loopback cannot be executed.
• Although in the Modbus specification, slave addresses
from 1 to 247 are used, if you use slave addresses from
250 to 254 on the master side, you can execute a
simultaneous broadcasting only to the specific slave
addresses. (The slaves do not return responses. This
function is valid only for writing commands (05h, 06h,
0Fh, 10h).)
Slave address Slave address for checking
Function code Function code for checking
Query data Answering data
Error check (CRC-16) Error check (CRC-16)
Slave Address Transmission Destination
250 (Fah) Simultaneous broadcasting to slave addresses 01 to 09.
251 (FBh) Simultaneous broadcasting to slave addresses 10 to 19.
252 (FCh) Simultaneous broadcasting to slave addresses 20 to 29.
253 (FDh) Simultaneous broadcasting to slave addresses 30 to 39.
254 (FEh) Simultaneous broadcasting to slave addresses 40 to 247.