39
W&T The serial combi-port
Subject to error and alteration
Operation modes
The DIL switches are used to set the following modes:
• RS422, RS485 4-wire bus master
Provides one data and handshake channel each in each
direction. The RS422/485 drivers and receivers are always
active in this mode.
• RS485 4-wire with automatic control
One data channel is available in each direction. The RS485
driver chip is automatically activated each time data is
sent out and then disabled when data is finished sending.
The receive channel is always active in this mode.
• RS485 2-wire bus with automatic control
One data channel is available in each direction. The RS485
driver chip is automatically activated each time data is
sent out and then disabled when data is finished sending.
The receive channel is deactivated when the driver is on,
and on when the driver is disabled.
Handshake for RS485 modes
RS485 bus systems do not use flow control in the traditional
sense for data integrity, but rather a logical protocol. The
handshake procedure for the Com-Server must therefore be
set to NO (see The serial parameters (Menu: UART Setup).
Terminating
All RS485 modes require a termination network on the bus
sytem which ensures a defined rest state in the high-ohmic
phases of bus operation. Connection of the bus system with
a termination network can be done in the interface by closing
the DIP switches 6 and 7 on the module:
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