12
NT579-NT579 RS485
TECSYSTEM SHANGHAI
19) FRONT PANEL
Keyboard
Messages Alarms
Display
FIGURE 1
Keyboard
Messages
DATA TRANSMISSION ON MODBUS NETWORK
The MODBUS INSIDE option allows to connect NT579 monitoring unit with
a RS485 network with Modbus RTU protocol in order to read and write the
data shown in the table MODBUS MAPPING at pag.13. The unit is always
in slave mode.
RS485 ELECTRICAL CONNECTIONS
As far as the signal cable to be used in order to ensure a proper network
working is concerned, we recommend to follow what laid down by EIA
RS485 standard which suggests to use a 24AWG duplex cable.
The duplex cable which connects all the units in RS485 could require the
activation of the 120 ohm termination on the last unit of the series.
Connect the duplex cable paying attention to polarities and lay the network
avoiding to make sharp bends or ring windings in order not to modify the
line impedance.
If necessary, also the GND terminal for grounding is available
DATA FRAME
The frame in asynchronous transmission is composed of: 1 start bit, 8 data
bits, 1 parity bit (even or odd, if the parity has been set) and 1 stop bit (2
stop bit if no parity is selected).
Admitted baud rates are: 2400, 4800, 9600, 19200 and 38400 b/s.
Where no otherwise specified, the word length (DATA) is of 16 bits.
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