User`s manual

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 40