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Modbus RTU connection:
Connection Port
Each device [MASTER or SLAVE] has a connection port with 2 terminals that are used to
communicate with that particular device over MODBUS RTU
–
RS485. These terminals are mostly
marked as A [or DATA +] and B [or DATA -]. The cabling is done such that all these devices are
connected in parallel. This means that all the A terminals should be connected together and all the B
terminals should be connected together
QUICK TIP-
Reversing the ‘A’ and ‘B’ connections of a device can lead to NOT being
able to
communicate with that device. In many cases, the whole communication systems can stop working
owing to the reverse polarity [voltage] found on the terminals of incorrectly connected device
In order to avoid this problem, it is recommended that the cable of same color should be used to
connect all A terminals together and similarly cable of same color [but different that the color used
for A] to be used to connect all B terminals together.
Connection between the devices
The easiest and the best way to connect the devices in a MODBUS RTU
–
RS485 communication is
using DAISY CHAIN method. It is shown below.
Any other way of connecting the devices together is
not recommended as it might cause communication issues or damage to the overall system.
