求助---有关SP339EER1-L的问题

wunai

1 O* V4 Y" T+ }% ~- _0 ]请问SP339EER1-L芯片的17号脚和12号脚有什么作用

超級狗

請針對看不懂的部份提出。

{:soso_e132:}

bluskly

这个片子我用过。我是用来把uart转成RS422和RS232输出。

wunai

bluskly 发表于 2013-9-10 11:28
这个片子我用过。我是用来把uart转成RS422和RS232输出。

$ ~' W$ k! ]9 [9 @: ?1 v. ]我需要用这个芯片实现RS232，RS485，RS422的自适应选择，我想问问17号脚要拉高还是拉低

wunai

超級狗 发表于 2013-9-10 11:17
請針對看不懂的部份提出。

8 o8 Y$ P- v$ \- H7 c. c) W我需要用这个芯片实现RS232，RS485，RS422的自适应选择，我想问问17号脚要拉高还是拉低

超級狗

4 ~) ?+ E% v' W) l4 Z
踢哀（TI）RS-422/RS-485 技術資料

, R7 A: T9 ]/ ^+ x; h* u( [2 [Selected RS-422 Electrical Specifications
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 Z_T. The termination impedance should be equal to the characteristic impedance of the cable, Z_o, and is used only once at the end of the cable. Because matching termination impedance to Z_o 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
greater than 200 kbps (10⁸/500).
, k) [) }3 D  x" S) G! R4 S
解乎？

2 `( h2 U+ G( _  m5 G1 I- _; l{:soso_e116:}