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