National Instruments 3.22E+04 Manual Do Utilizador
Chapter 4
Using Your Serial Hardware
4-2
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Note
Signal names with an overscore, such as DTR, indicate that the signal is active low.
Four-Wire Mode
Use the four-wire mode for most full-duplex systems. In this mode, the
transmitter and receiver are always enabled. This mode is the default.
transmitter and receiver are always enabled. This mode is the default.
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.
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 the packets
sent from your transmitter.
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 the packets
sent from your transmitter.
Table 4-1. Transceiver Control Modes
Mode
Transmitter
Receiver
Four-wire mode
Always enabled
Always enabled
Two-wire mode:
DTR with echo
DTR with echo
Enabled with
DTR unasserted
DTR unasserted
Always enabled
Two-wire mode:
DTR controlled
DTR controlled
Enabled with
DTR unasserted
DTR unasserted
Enabled with
DTR asserted
DTR asserted
Two-wire mode:
TXRDY auto control
TXRDY auto control
Enabled with
TXRDY asserted
TXRDY asserted
Enabled with
TXRDY unasserted
TXRDY unasserted