Chapter 4
Using Your Serial Hardware
PCMCIA Serial for Windows 98/95
4-2
©
National Instruments Corporation
Two-Wire Mode: DTR with Echo
Use this mode in half-duplex systems where the DTR (Data Terminal
Ready) line must control the transmitter. In the DTR-with-echo mode, the
transmitter is tri-stated when the DTR signal of the UART (Universal
Asynchronous Receiver/Transmitter) is asserted. To transmit, your
application must first clear the DTR bit to enable the transmitter. After the
data is fully transmitted, your application once again sets the DTR bit to
disable the transmitter. Because the receiver is always enabled in this
mode, you not only receive packets from other devices, you also receive the
packets sent from your transmitter.
Two-Wire Mode: DTR Controlled
This mode is similar to the two-wire, DTR-with-echo mode. Use this mode
in half-duplex systems where the DTR line must control the transmitter.
Although this mode uses the same method as the DTR-with-echo mode to
control the transmitter, the hardware automatically disables the receiver
whenever the transmitter is enabled. Thus, you do not receive packets that
you have transmitted.
Two-Wire Mode: TXRDY Auto Control
In this mode, the hardware transparently enables the transmitter and
receiver in a two-wire system. This mode removes the burden of flow
control from the user software. 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 packets that you
have transmitted.
Note
It is recommended that you use the two-wire
TXRDY
auto control mode when
you are communicating with a two-wire device. 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 communications in
two- or four-wire modes, refer to the section
in
Appendix B,
.
Summary of Contents for PCMCIA Serias
Page 1: ...PCMCIA 485 2...
