©
National Instruments Corporation
4-1
Serial for Windows NT
Using Your Serial Hardware
4
Chapter
This chapter describes how to set the hardware transceiver control mode
for your RS-485 interfaces and lists some general programming
requirements.
Advanced Transceiver Control (AT-485/PCMCIA-485)
The AT-485 boards and PCMCIA-485 cards support four modes of
hardware transceiver control. (Transceiver modes apply only to these
interfaces.) You can use hardware flow control to enable and disable your
transmitters and receivers to work on different bus topologies. Table 4-1
lists the status of the transmitters and receivers under each of the
transceiver control modes.
Table 4-1.
Transceiver Control Modes
Mode
Transmitter
Receiver
Four-wire mode
Always enabled
Always enabled
Two-wire mode:
DTR
with echo
Enabled with
DTR
unasserted
Always enabled
Two-wire mode:
DTR
controlled
Enabled with
DTR
unasserted
Enabled with
DTR
asserted
Two-wire mode:
TXR DY
auto control
Enabled with
TXR DY
asserted
Enabled with
TXR DY
unasserted
Note:
Signal names with an overscore, such as
DTR
, indicate that the signal is
active low.
