Chapter 4 Using Your Serial Hardware
© National Instruments Corporation 4-3 PCI Serial for Windows Me/9x
Two-Wire Mode: TXRDY Auto Control
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.
Note 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,
itreduces 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
Serial Communication Issues section in Appendix A, Serial Port Information.
Setting the Transceiver Control Mode
To set the transceiver control mode, use the Windows Me/9x Device
Manager. For instructions on how to use the Device Manager, refer to
Chapter3, C onfiguration. 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.