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14/09/2016
23/09/16 17.56
Gateway MODBUS-to-Opentherm MB-OTG
Technical manual
2
Installation
The gateway must be connected as indicated in the following scheme:
Mod. MB-OTG
Notes:
OpenTherm connections
are not
polarized, so the respective cables can be inverted.
Gateway’s OpenTherm channel is optoisolated from the MODbus side.
MODbus interface
is not
optoisolated respect to the Gateway’s Power Supply, so typically the
Master and Gateway are powered by the same Power Supply, or from Power Supply with shorted
references.
The polarity definition on the “A” and “B” wires is arbitrary because it does not exist a unique
standard for the MODbus; other companies may use different conventions (for example, “+” and
“-“). Therefore, in case of no communication, try to invert the connection on the two poles “A” and
“B” and check the communication state by controlling the “BUS” LED (for more information read
paragraph 3.1).
Attention !
OpenTherm protocol is a point-to-point protocol: only 1 Boiler must be connected to a MB-OTG; the
connection of two or more Boilers on the same MB-OTG may cause damage to the Boiler and/or the
Gateway interface.
