Modbus Over A Serial Interface; Modbus Slave Communication Over An Rs422/485 Serial Interface - ECOLAB Versatronic Modbus Beschreibung

6

Modbus over a serial interface

6.1

Modbus slave communication over an RS422/485 serial interface

The Versatronic has, in the base version, 1 serial interface RS422/485 (COM 1 on the
base unit). In addition, a RS422/485 interface can be retrofitted in slot 'COM 2' as an
optional board.
These interfaces can be used to connect the device as a Modbus slave to up to 2 bus
systems. In each bus, 1 master can access the Modbus data of the Versatronic on each
bus, all slave devices must have unique device addresses in the range of 1 to 254.
The master is not addressed.
A scanning cycle on a bus proceeds with the following timing:
Fig. 2: A scanning cycle on a bus proceeds with the following timing
Internal waiting period of the device before checking the data query and the internal processing time:
min.: 5 ms
t
1
typically: 5 to 35 ms
max.: 35 ms or the set 'minimum response time'
t
Waiting period that the master must observe before it starts a new data query with RS485: 35 ms
2
NOTICE!
The minimum response time can be set in the configuration.
Device menu > Configuration > Serial interface > Serial interface 1 to 2
This set time must elapse before a response is sent (0 to 500 ms). If
processing of a query from a master is completed in the slave before the
minimum response time has elapsed, the response is not sent until the
"minimum response time" has elapsed.
With an RS485 interface, the minimum response time that can be set is
needed by the master to switch the interface driver from send to receive.
Within t
may be generated by the master. Queries during t
the slave. Requests during the response time invalidate all the data
currently on the bus.
The terminating code after a data query or data response is 3 characters
long. The time needed for these 3 characters depends on the baud rate.
and t and during the response time of the slave, no data queries
1 2
Modbus over a serial interface
and t
1
37
are ignored by
2
417102397 Rev. 1-10.2019