National Instruments 3.22E+04 用户手册

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In this mode, the serial hardware transparently enables the transmitter and 
receiver in a two-wire system. Use this mode to remove the burden of flow 
control from your application. By connecting the transmitter to the 
TXRDY (Transmit Ready) line, the hardware enables the transmitter for 
each byte to be transmitted. Also, the hardware disables the receiver 
whenever the transmitter is enabled, so you do not receive the packets sent 
from your transmitter.

When you are communicating with a two-wire device, National Instruments 

recommends that you use the two-wire TXRDY auto control mode. Because this mode 
handles the transmitter/receiver enabling for a two-wire connection in your hardware, 
it reduces the software overhead required to perform this operation in your application 
program.

For more information about serial communication in two- or four-wire modes, refer to the 

 section in Appendix A, 

.

To set the transceiver control mode, use the Windows Me/9x Device 
Manager. For instructions on how to use the Device Manager, refer to 
Chapter 3, 

. The mode you select in the Device Manager is 

automatically configured when you open a port on a serial interface.

You can also set the hardware transceiver control mode from within a DOS 
application. For each port you want to control, write the control byte for the 
mode you want to select to the scratch register of the UART. Table 4-2 
shows the control bytes for each mode.