Question

帮我翻译成英文 谢谢

五、RS-422与RS-485传输线上匹配的一些说明
对RS-422与RS-485总线网络一般要使用终接电阻进行匹配。但在短距离与低速率下可以不用考虑终端匹配。那么在什么情况下不用考虑匹配呢？理论上,在每个接收数据信号的中点进行采样时,只要反射信号在开始采样时衰减到足够低就可以不考虑匹配。但这在实际上难以掌握,美国MAXIM公司有篇文章提到一条经验性的原则可以用来判断在什么样的数据速率和电缆长度时需要进行匹配：当信号的转换时间（上升或下降时间）超过电信号沿总线单向传输所需时间的3倍以上时就可以不加匹配。例如具有限斜率特性的RS-485接口MAX483输出信号的上升或下降时间最小为250ns,典型双绞线上的信号传输速率约为0.2m/ns（24AWG PVC电缆）,那么只要数据速率在250kb/s以内、电缆长度不超过16米,采用MAX483作为RS-485接口时就可以不加终端匹配。
一般终端匹配采用终接电阻方法,前文已有提及,RS-422在总线电缆的远端并接电阻,RS-485则应在总线电缆的开始和末端都需并接终接电阻。终接电阻一般在RS-422网络中取100Ω,在RS-485网络中取120Ω。相当于电缆特性阻抗的电阻,因为大多数双绞线电缆特性阻抗大约在100～120Ω。这种匹配方法简单有效,但有一个缺点,匹配电阻要消耗较大功率,对于功耗限制比较严格的系统不太适合。
另外一种比较省电的匹配方式是RC匹配。利用一只电容C隔断直流成分可以节省大部分功率。但电容C的取值是个难点,需要在功耗和匹配质量间进行折衷。
还有一种采用二极管的匹配方法。这种方案虽未实现真正的“匹配”,但它利用二极管的钳位作用能迅速削弱反射信号,达到改善信号质量的目的。节能效果显著。

Answer 1

5, RS-422 and RS-485 transmission lines that match the description of some
The RS-422 and RS-485 bus network in general resistance to the use of terminating match. But in the short distance and low rates can not consider the terminal match. So under what circumstances do not have to consider matching it » In theory, each receive data signals in the mid-point of sampling, as long as the signal reflection at the beginning of sampling at the low enough to decay can not consider the match. But in practice difficult to grasp, the United States MAXIM companies have an empirical articles referred to the principle can be used to determine what kind of data rate and cable length of time needed to match: When the signal conversion time (rise or fall time) Electrical signals along the bus more than a one-way transmission time for more than three times when it can not match. For example, has limited the slope of the RS-485 interface MAX483 output increase or decrease the minimum time for the 250 ns, typical twisted pair on the signal transmission rate of about 0.2 m / ns (24AWG PVC cable), then as long as the data rate of 250 kb in / s within the length of cable is not more than 16 meters, MAX483 used as a RS-485 interface at the terminal can not match.
General terminal match by terminating resistance methods, Qian Wenyi mentioned, RS-422 bus lines in the remote access and resistance, RS-485 bus lines should be in the beginning and end are subject to termination and resistance. Termination of the resistance in general RS-422 network from 100 Ω, in the RS-485 network from 120 Ω. Impedance of the cable equivalent of resistance, because most twisted pair cables impedance of about 100 ~ 120 Ω. This matching method is simple and effective, but there is a drawback, matching resistance to high power consumption, more stringent restrictions on the power system is not suitable.
In addition a more efficient way of matching the RC match. Use of a capacitor C cut off most of DC components can save power. However, the value of capacitance C is a difficult, power consumption and the need to match the quality of a compromise between.
There is also a diode using the matching method. Such programmes not yet a real "match", but its use diode clamp role of the rapid weakening reflection signal to improve signal quality. Energy-saving significantly.

Answer 2

这么多 呵呵 难呢 用金山快译吧 不过翻译出的结果很差的 要很大程度上改的

Answer 3

切,都是复制Goole里面的.没意思!

Answer 4

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