NI SCXI-1125电压输出模块,SCXI-1125配置手册
EIA-232-D标准是最常见的终端/计算机和终端/调制解调器接口，但尚未完全理解。
这可能是因为并不是所有的线都被清楚地定义，而且许多用户认为没有必要在他们的应用。设计师通常只考虑自己的设备，但最先进的技术是计算机对计算机或计算机对模型操作。系统应易于连接到任何其他系统系统EIA-232-D标准最初由贝尔公司开发通过调制解调器连接终端的系统。多次握手为此目的包括了线路。
NI SCXI-1125电压输出模块虽然握手是在许多应用中没有必要，线路本身仍然是一部分因为它们便于故障排除。表E-1列出了标准EIA-232-D互连。到正确解释这些信息，记住EIA-232-D是用于将终端连接到调制解调器。当计算机在没有调制解调器的情况下相互连接，其中一个必须配置为终端（数据终端设备：DTE）和其他作为调制解调器（数据电路终端设备：DCE）。自从计算机通常配置为与终端一起工作在大多数情况下被配置为调制解调器。
对于高电平，信号电平必须介于+3和+15伏之间，并且低电平在-3到-15伏之间。并联连接装置
可能产生超出范围的电压，与EIA-232-D相反规范。有几个级别的一致性可能适用于典型EIA-232-D互连。最低限度要求是两条数据线和一个接地。完整的EIA-232-D的实施需要12条线路；它可容纳：❏ 自动拨号❏ 自动应答❏ 同步传输信号自适应
经常实现的一组握手信号是RTS和CT。在许多系统中使用电流互感器来抑制传输，信号高。在调制解调器应用程序中，RTS被逆转150微秒后返回为CT。RTS可编程在某些系统中，使用较旧的202型调制解调器（一半双面打印）。在某些系统中，电流互感器用于为以下各项提供流量控制：避免缓冲区溢出。如果使用调制解调器，这是不可能的。它是通常需要通过将CT连接到RTS或一些+12伏电源，如图E-1所示的电阻器。电流互感器也经常跨接至MC1488门，该门具有
输入接地（为此提供栅极）。
The EIA-232-D standard is the most common terminal/computer
and terminal/modem interface, and yet it is not fully understood.
This may be because not all the lines are clearly defined, and many
users do not see the need to follow the standard in their
applications. Often designers think only of their own equipment,
but the state of the art is computer-to-computer or computer-tomodem operation. A system should easily connect to any other
system.
The EIA-232-D standard was originally developed by the Bell
System to connect terminals via modems. Several handshaking
lines were included for that purpose. Although handshaking is
unnecessary in many applications, the lines themselves remain part
of many designs because they facilitate troubleshooting.
Table E-1 lists the standard EIA-232-D interconnections. To
interpret this information correctly, remember that EIA-232-D was
intended to connect a terminal to a modem. When computers are
connected to each other without modems, one of them must be
configured as a terminal (data terminal equipment: DTE) and the
other as a modem (data circuit-terminating equipment: DCE). Since
computers are normally configured to work with terminals, they
are said to be configured as a modem in most cases.
Signal levels must lie between +3 and +15 volts for a high level, and
between -3 and -15 volts for a low level. Connecting units in parallel
may produce out-of-range voltages and is contrary to EIA-232-D
specifications.There are several levels of conformance that may be appropriate for
typical EIA-232-D interconnections. The bare minimum
requirement is the two data lines and a ground. The full
implementation of EIA-232-D requires 12 lines; it accommodates:
❏ Automatic dialing
❏ Automatic answering
❏ Synchronous transmission Signal Adaptations
One set of handshaking signals frequently implemented are RTS
and CTS. CTS is used in many systems to inhibit transmission until
the signal is high. In the modem application, RTS is turned around
and returned as CTS after 150 microseconds. RTS is programmable
in some systems to work with the older type 202 modem (half
duplex). CTS is used in some systems to provide flow control to
avoid buffer overflow. This is not possible if modems are used. It is
usually necessary to make CTS high by connecting it to RTS or to
some source of +12 volts such as the resistors shown in Figure E-1.
CTS is also frequently jumpered to an MC1488 gate which has its
inputs grounded (the gate is provided for this purpose).
