LSI LASTEM M-Log – User’s manual
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For more informations about TTY protocol see INSTUM_00728_en manual reported on LSI
LASTEM products DVD (MW6501).
5.6.5
Modbus Protocol
Modbus is a serial communication protocol used in industrial circle; it allows the communication
between one
master
(usually PC) and one or more
slave
(devices for measurement, check or PLC)
connected to the same network. Modbus sets-up the
master
and
slave
’s modes to start and stop the
communication, it settles the modes for messages exchange and errors identifying too. Only
master
can start the communication.
There are two protocol versions: one serial version (RS-232 or RS-485) and one Ethernet version.
The serial version includes two different communication modes: one RTU mode (where the data are
packet in Hexadecimal format) and one ASCII mode (where the data can be easily read). In
Ethernet version (like the RTU version) the protocol’s packets are inside TCP/IP packets.
Every network device has its univocal address. A Modbus command includes the Modbus address
of the instrument which want communicate with. Only this instrument will answer to the command,
even though all instrument receive it. All Modbus commands include check information, that assure
the correct reception of the command. The base commands can ask to a
slave
to change one value
into one of its statuses or to return one or more values included into its registers.
E-Log looks like
slave
and implements part of the industrial Modbus protocol in RTU version on
serial port RS-232.
For more informations about Modbus protocol see INSTUM_00728_en manual reported on LSI
LASTEM products DVD (MW6501).
5.6.6
M-Log connected like master-slave mode
It’s possible use two M-Log cascading, that is master/slave mode, especially when the number of
physical inputs required by the application is higher than the number of physical inputs supplied by
one M-Log datalogger. So we call
master
instrument the M-Log connected to host through direct
connection or through communication apparatus, while
slave
instrument is connected only to master
instrument. Using this configuration mode the slave instrument is a real multi-parametric serial
sensor (from master datalogger’s point of view).
In order to configure the system like master/slave mode follow the instructions below:
1.
Physical connection:
Connect the serial port 2 of both dataloggers using null modem cable (LSI LASTEM
code ELA121) or serial cable (LSI LASTEM code ELA105) with null modem
adapter;
Connect the serial port 1 of M-Log master with the host through direct connection or
through one communication apparatus.
2.
During configuration through 3DOM software:
configure the slave instrument using only its measures (i.e. the measures that take-up
their physical inputs) and don’t setup any elaborations;
