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RS-422/485
Driver
RS-422/485
Driver
+
-
+
-
Data Out
Aux Out
Active Low
Output Enable
3 Options:
Half Duplex
16C550
-RTS
-DTR
NOTE:
One of these three options must be selected via
software configuration. Full duplex operation is
the default mode.
Full Duplex
MUX
Figure 8. RS-422/485 Driver Enable Options
If RTS is selected as the signal to enable the output drivers, setting 'bit 1' of the Modem Control
Register (to logic '1') will enable the output drivers and clearing 'bit 1' of the Modem Control
Register (to logic '0') will force the outputs into a high impedance state.
Similarly, if DTR is chosen as the signal to enable the output drivers setting 'bit 0' of the Modem
Control Register (to logic '1') will enable the output drivers and clearing 'bit 0' of the Modem
Control Register (to logic '0') will force the outputs into a high impedance state.
Selection of half duplex mode operation is dependent upon the configuration software and/or the
operating system used. Each of these,
however, ultimately control the half duplex mode by accessing the PCMCIA Configuration
Register on the QSP-200/300.
CAUTION:
When operating in half duplex mode, the transmitter output drivers
must be
disabled before receiving and information. Failure to do so
will result in two output drivers being connected together which
may cause damage to the adapter, the computer, and/or the
peripheral equipment.
QSP-200/300 User's Manual 39