Westermo MA-42 - Manual (Page 6)

12 6042-2002
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The MA-42 uses the RS-422/485 interface.
RS-422/485 was designed for multidrop applications. When a system is installed it should
form a bus structure (see diagrams). Star shaped networks should never be created,
there are other Westermo products designed to work in star net applications. For
correct installation an RS-422/485 network should be terminated at the correct points.
The recommendation is to terminate the receivers at both end of network.
See diagrams for details of how this is done with RS-485 (2 wire) and RS-422 (4 wire).
On 4 wire systems when the MA-42 is working as a slave, the transmitter is linked to
the same bus as all the other slaves transmitter. A status signal (RTS or DTR) is used to
control the MA-42’s transmitter, to ensure that only one slave is active on the bus at the
same time. The status signal is also used to control direction for RS-485 (2 wire) trans-
mission.
If any problems do occur on set up of the MA-42, the LED’s will be helpful.
• PWR: The unit has power.
• RD: Data received on the RS-422/485 interface.
• DCD: Simulated carrier due to the setting of S2.
• CTS: Follows RTS.
• RTS: Indicates that the RS-422/485 transmitter is activated.
• TD: Data received on the RS-232 interface.