B&B Electronics MES1A - Manual (Page 16)

Hardware Overview
Manual Documentation Number: MES1A/MES1B-2106m PN7138-rev001
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
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Figure 4. MES1B Serial Connector
RS-422/485 Four-Wire Mode
When the MES1B is configured to operate in RS-422/485 four-wire
mode (RS-422/485 switch in the left position) its receive terminals
are connected to the transmit terminals of the Modbus device it is
communicating with. Its transmit terminals are connected to the
receive terminals of the Modbus device it is communicating with.
Figure 5. RS-422/485 Four-Wire Connection
RS-485 Two-Wire Mode
When the MES1B is configured to operate in RS-485 two-wire
mode (RS-422/485 switch in the right position) the two-wire RS-
485 two-wire communications cable pair is connected to Terminals
TDB and TDA. The communications cable ground/shield is
connected to GND.