©
National Instruments Corporation
4-1
PCMCIA Serial for Windows 95
4
Using Your Serial Hardware
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 for the PCMCIA-485
The 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.
Note
Signal names with an overscore
,
such as
, indicate that the signal is active
low.
Four-Wire Mode
Use the four-wire mode for most full-duplex systems. In this mode, the
transmitter and receiver are always enabled. This mode is the default.
Table 4-1.
Transceiver Control Modes
Mode
Transmitter
Receiver
Four-wire mode
Always enabled
Always enabled
Two-wire mode:
with echo
Enabled
with
unasserted
Always enabled
Two-wire mode:
controlled
Enabled
with
unasserted
Enabled with
asserted
Two-wire mode:
auto control
Enabled with
asserted
Enabled
with
unasserted
DTR
DTR
DTR
DTR
DTR
TXRDY
TXRDY
TXRDY
DTR
