National Instruments PCI-8430, Manual

Page: 118 / 237

USB-232 Transceiver Control
The USB-232 two and four-port hardware supports both DTE and DCE
transceiver modes. By default, the RS-232 transceiver mode is forced to
DTE, but you can adjust this in two ways:
Use the Advanced tab in MAX. To set the transceiver mode to be
used whenever a port is opened, select the desired mode from the
transceiver mode pull-down menu.
Change the transceiver mode programmatically by making a
DeviceIoControl function call to the serial driver.
The following table describes the RS-232 modes.
RS-232 Modes
RS-232
Mode
Description
Force
DTE
(Default) The transceiver is forced into DTE mode
Force
DCE The transceiver is forced into DCE mode
Auto
232 The transceiver automatically switches between DTE and DCE
modes about four times a second until a valid RS-232 signal is
detected
Note When using Auto232, if you connect two serial ports set to
Auto232, or if valid RS-232 signals are present in both modes, the
final mode may be either DTE or DCE.
Note A valid RS-232 signal is defined as at least one valid RS-232
voltage detected on any receiver pin (RXD, CTS, DSR, RI, or
DCD).
The USB-232 hardware also allows you to set and retrieve the state of
the of the Ring Indicate (RI) and Data Carrier Detect (DCD) lines along
with the Transceiver Mode.
Setting the RS-232 Transceiver Mode with DeviceIoControl
Setting Ring Indicate (RI) and Data Carrier Detect (DCD) with
DeviceIoControl