Quatech DSP-200/300 - Manual (Page 46)

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 DSP-200/300.
CAUTION:
When operating in half duplex mode, the transmitter output drivers
must be disabled before receiving any 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.
6-4 DSP-200/300 (Rev. I and later) User's Manual