|
|
本帖最后由 超級狗 于 2013-9-10 17:38 编辑 ' ?. q. Z- T5 @2 ?0 p- E- T
2 ~# j, Y: s8 `, ^1 \踢哀（TI）RS-422/RS-485 技術資料# Y; }/ M6 U. u/ o8 U7 _
; `, d- N% V. i* Q9 l
Selected RS-422 Electrical Specifications2 g( `! R' F" W" c
The balanced-voltage digital interface is shown in Figure 1. The driver (or generator) is labeled D, the receiver is labeled R, and the termination impedance is ZT. The termination impedance should be equal to the characteristic impedance of the cable, Zo, and is used only once at the end of the cable. Because matching termination impedance to Zo often is difficult to achieve and is application dependent, typically, ±20% is sufficient. Also, up to nine additional receivers can be placed along the cable from points A and B to points A' and B', respectively. No restriction on maximum cable length is imposed by the RS-422 standard. Taking this into account, systems of up to 1 km are not uncommon, with signaling rates no higher than about 100 kbps. Speed and cable lengths work against each other. In other words, the longer the cable, the slower the signaling rate must be, while data can be transmitted faster on shorter cables. As a rule of thumb, the data signaling rate (in bps) multiplied by the cable length (in meters) should not exceed 108. For example, a system with a cable measuring 500 m should not transmit data at speeds
3 A1 M' u; u* e. [greater than 200 kbps (108/500).
* g& i9 Q0 C8 ?. [3 M1 S& Q7 M
) J) }* y6 o f+ h) [. o* K( ?: |解乎？
' ]) d4 L$ }* Z" z( E$ W' Q4 b; I, \
{:soso_e116:} |
|
/1 
发表于 2013-9-9 16:39
QQ好友和群
QQ空间
腾讯微博
腾讯朋友
微信
收藏
支持！
反对！
发表于 2013-9-10 11:17
楼主