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MCS7840
USB-2.0 to Four Serial Ports
Page 20
Rev.
1.2
RS-422 / RS-485 Mode Support
Two additional modes of serial port operation are supported, these are:
•
RS-422 Mode – Full Duplex Serial Port for industrial applications
•
RS-485 Mode – Half Duplex Serial Port for industrial applications
RS-485
The RS-485 mode can be set using the Scratch
Pad Register bit[6] and bit[7] for each serial port.
This mode is a half duplex mode and the external
transceiver is controlled for transmission or
reception using the enable signal.
Scratch Pad
Bit[7]
Scratch Pad
Bit[6]
Operation
Summary
0X
RS-485 Mode
Disabled
10
RS-485 Mode
Enabled,
DTR High = Rx
DTR Low = Tx
11
RS-485 Mode
Enabled
DTR Low = Rx
DTR High = Tx
This is the
default
selection when
RS485 mode
is selected
through driver
property sheets.
RS-422
This is the full duplex mode.
This mode will work without the use of the DTR
signal for external transceiver control.
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