Laser Pointer User Manual

Chapter 4 Using Your Serial Hardware

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,

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

Serial Communication Issues section in Appendix A, Serial Port Information.

Setting the Transceiver Control Mode

The recommended method for setting the transceiver control mode is

with the serial configuration utility located in the Windows Me/9x

Device Manager. For more information, refer to the View or Change

Communication Port Settings section in Chapter 3, Configuration.

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.

Table 4-2.

Transceiver Mode Control Bytes

Transceiver Mode Control Byte

Four-wire mode 0x00

Two-wire mode: DTR with echo 0x01

Two-wire mode: DTR controlled 0x02

Two-wire mode: TXRDY auto control 0x03