10
T2612 UNI
TECSYSTEM S.r.l ®
25) MODBUS RS485 INTRODUCTION (ONLY FOR MODEL T2612 AND T2612AD)
The T2612 implements a sub-whole of the standard serial communication protocol Modicon
Modbus RTU. The Modbus T2612 employs a RS485 connection with 2 twisted-pair wire
hardware; with this mode it is allowed to connect up to 32 monitoring units on the same
wiring. The T2612 is always in slave mode.
26) ELECTRICAL CONNECTION
The twisted-pair wiring that connects all the units with RS485 needs 120 ohm terminal resis-
tors on the opposite side of the master. To enable the terminal resistor connect the “END”
terminal with the “TX” terminal (-) on the “serial output” terminal board.
Important Note : the twisted-pair wires must be connected according to the polarity;
then, all the (+) with the (+) and all the (-) with the (-).
As far as the signal cable to be used to guarantee a correct working of the network is con-
cerned, we suggest to follow what is provided for by EIA RS485 standard which advises the
use of a 24AWG loop.
In order not to affect the line impedance, connect the loop keeping into consideration the
polarities and lay the network avoiding to create sharp bends or ring windings.
In case of necessity, it is also available the GND dead ground terminal.
27) DATA FRAME
The asynchronous transmission frame is made of 1 bit of START, 8 bit Data, 1 bit of parity
(if enabled) and 1 bit of Stop.
The allowed Baud rates are: 2400, 4800, 9600 and 19200; the addresses are from 0 to 32
(0 for non-connected).
The DATA are “16bit” length where no specified.
28) DATA PACKET
A complete question/answer sequence is as follows :
Question from the master :
SLAVE ADDRESS - 1byte
FUNCTION CODE - 1byte
DATA - variable, it depends on the function code
CRC - 2 bytes
Answer from slave :
SLAVE ADDRESS - 1byte
FUNCTION CODE - 1byte
DATA - variable, it depends on the function code
CRC - 2 bytes
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