485A2應(yīng)用的RS-485多機(jī)通信的典型接線圖以及485A2 產(chǎn)品圖，如果串口設(shè)備只有RS-485口則可以配接485A2 。若每一段RS-485的距離為1200米和128個(gè)，則整個(gè)RS-485系統(tǒng)的距離達(dá)到（N?1200米）、節(jié)點(diǎn)數(shù)達(dá)到（N?128）?？梢钥闯觯褂昧?85A2的RS-485總線布線極其簡潔。最遠(yuǎn)兩端可以用485A，也可以用485A2。注意整個(gè)RS-485系統(tǒng)共用GND線。
2、RS-485多機(jī)通信節(jié)點(diǎn)數(shù)的極限
DS200SVMAG1 假設(shè)RS-485通信的地址編碼為8位，那么最多的節(jié)點(diǎn)數(shù)就是2^8=256;假設(shè)RS-485通信的地址編碼為10位，那么最多的節(jié)點(diǎn)數(shù)就是2^10=1024。10位已經(jīng)多到極少用到。這個(gè)總線中的RS-485節(jié)點(diǎn)數(shù)的極限完全取決于通信軟件 ，與總線中所接的RS-485中繼轉(zhuǎn)換器個(gè)數(shù)沒有關(guān)系。實(shí)際上，因?yàn)槭躌S-485接口芯片性能的限制，每一段RS-485目前最多接128個(gè)節(jié)點(diǎn)，所以要達(dá)到256個(gè)的極限就得至少接一個(gè)485A2中繼轉(zhuǎn)換器，要達(dá)到1024極限就要至少8個(gè)485A2中繼轉(zhuǎn)換器。
3、DS200SVMAG1完全失敗的RS-485通信距離的理論極限
假設(shè)波特率為9600bps，就是每秒9600位。每個(gè)數(shù)據(jù)有1個(gè)起始位、8個(gè)數(shù)據(jù)位、1個(gè)校驗(yàn)位、1個(gè)停止位，一共11位。也就是傳輸一個(gè)數(shù)據(jù)（1byte）的時(shí)間是11/9600=0.001145s。在這個(gè)時(shí)間內(nèi)電磁波的傳輸距離（也就是光速為299792458m/s ）為343512米，即343.5千米。
DS200SVMAG1
DS200SVIAG1
DS200SVAAG
DS200STCAG1A
DS200STCAG1
DS200STCAG
DS200SVAAG1A
DS200TBQAG1ABB
DS200TBQAG1A
DS200TBQAG1
DS200TBQAG
DS200TBPXG1AAA
DS200TBPXG1A
DS200TBPXG1
DS200TBPXG
DS200TBCBG1AAA
DS200TBCBG1A
DS200TBCBG1
DS200ADPAG1A
DS200ADMAH1A
DS200ADGIH1A
DS200ACNAG1A
DS200AAHAH2A
DS200AAHAH1A
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