Varec Network Adapter 4000, Installation And Operation Manual, Page: 53 / 80

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4000 Theory of Operation
When emulating an 1800 or 1900, battery low status can be reported as one of the dry-
contact inputs or as an invalid level.
Note! The ATT will accept but ignore the Raise/Lower Displacer commands.
7.11 Modbus Support over Mark/Space Host Interface
The ATT permits Modbus communications over the Mark/Space data highway. The
Modbus request message is placed into a Mark/Space message frame. The ATT
processes the request message and places the Modbus reply in a Mark/Space reply
frame.
This option is only available with systems using the Model 6840 Tank Polling Unit.
7.12 Compatibility with Varec Tank Polling Unit
The Mark/Space communications provided by the ATT are compatible with the Varec
Tank Polling Unit (TPU). This permits the ATT to be multi-dropped on the same Mark/
Space data highway as the Varec 1800, Varec 1900, and MFT/HIU devices.
If the EIA485 communications interface is installed in the ATT, it can be multi-dropped
on an EIA485 data highway, RTU 8130 along with any Modbus compatible device,
including the Model 6850 Field Interface Converter.