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RS-485ÊôÓÚOSIÄ£Ð͵ÄÎïÀí²ã£¨Physical Layer£©£¬ÆäµçÆøÌØÐԹ涨Ϊ2Ïß¡¢°ëË«¹¤¡¢Æ½ºâ´«ÊäÏß¶àµãͨÐŵıê×¼£¬ÊÇÓɵçÐÅÐÐҵлᣨTIA£©¼°µç×Ó¹¤ÒµÁªÃË£¨EIA£©ÁªºÏ·¢²¼µÄ±ê×¼¡£ÊµÏִ˱ê×¼µÄÊý×ÖͨÐÅÍø¿ÉÒÔÔÚÓеç×ÓÔëÉùµÄ»·¾³Ï½øÐг¤¾àÀë¸ßЧµÄͨÐÅ¡£ÔÚ¶à½Úµã×ÜÏßµÄÅäÖÃÏ£¬¿ÉÒÔÔÚÒ»¸öÍøÂçÉÏÓжà¸ö½ÓÊÕÆ÷£¬Òò´ËÊÊÓÃÓÚ¹¤Òµ»·¾³¡£Æä±ê×¼TIA/EIA-485-AÓÚ1998Äê3ÔÂ3ÈÕºË×¼¡¾1¡¿£¬×Ô´ËÖ®ºóÐí¶à¹¤ÒµÓ¦ÓÃÏà¼Ì²ÉÓÃRS-485×÷ΪͨÐŽӿڡ£
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1. ÖÇÄÜ»¯ [ÎÞ¼«ÐÔ£¨Polarity-Free£©RS-485]:
ÔÚ¹¤Òµ»·¾³ÖУ¬É豸µÄÐÂÉèÖᢹÊÕÏάÐÞ¡¢µ÷ÊԵȹ¤×÷ÖУ¬Ê©¹¤ÈËÔ±¿ÉÄÜ»á³öÏÖÅäÏß´íÎóµÄÇé¿ö¡£Ò»°ãRS-485µÄ×ÜÏßA/BÈç¹û·¢ÉúÏ໥½Ó´í£¬»áµ¼ÖÂͨÐÅÒì³££¬Èô²¼Ïß¾àÀë½Ï³¤£¬ÅŲéºÍÐÞÕý´íÎóµÄ½Úµã¿ÉÄܺķѴóÁ¿Ê±¼ä¡£¼øÓÚ´Ë£¬¾§ìͿƼ¼µÄAZRS5485N RS-485ÊÕ·¢Æ÷¾ßÓÐÎÞ¼«ÐÔ£¨Polarity-Free£©ÌØÐÔ£¬¼´Ê¹A/B×ÜÏß·¢ÉúÏ໥½Ó´í£¬Ò²Äܼì²â²¢×Ô¶¯ÐÞÕý£¬ÎÞÐèÈ˹¤ÊÖ¶¯ÐÞÕý£¬Ò²²»ÐèÒª¶îÍâµÄÈí¼þÉèÖ㬷ûºÏÃ÷ÈÕ¹¤³§µÄÖÇ»ÛÉý¼¶Ç÷ÊÆ¡£¡¾×¢£ºÔÚʹÓÃAZRS5485Nʱ£¬ÐèÒªÔÚMaster½ÚµãA/B·Ö±ðÉè¼ÆÉÏÀ£¨Pull-high£©ºÍÏÂÀ£¨Pull-low£©µç×裬¶øSlave½ÚµãÔò²»ÐèÒª£¬ÏêÇé²Î¼ûAZRS5485N Datasheet¡¿¡£
´ËÍ⣬É豸µÄÐÂÉèÖᢹÊÕÏάÐÞ»òµ÷ÊÔʱ£¬RS-485×ÜÏß¿ÉÄÜÍâ¶»òÓëÊ©¹¤ÈËÔ±½Ó´¥£¬AZRS5485N¾ßÓÐIEC 61000-4-2 ±15kV£¨½Ó´¥£©/ ±20kV£¨¿ÕÆø£©µÄ¾²µç·À»¤µÈ¼¶£¬¿ÉÓÐЧ·À»¤¾²µçÄÜÁ¿¶Ô×ÜÏߵijå»÷£¬¼õÉÙ¾²µçµ¼ÖµÄÉ豸²»Îȶ¨»ò¹ÊÕÏÒþ»¼¡£
| P/N | Max. Data Rate | IEC 61000-4-2 ESD for Bus (Contact/Air) |
Polarity-Free (ÎÞ¼«ÐÔ) |
| AZRS5485N | 10Mbps | ±15kV/±20kV | YES |
Table 1. ÎÞ¼«ÐÔ( Polarity-Free) RS-485
2. ½ÚÄÜ£¨¾ßÓÐShutdown¹¦ÄÜÇÒ3.3V¹©µçµÄRS-485):
½ÚÄÜÊǵç×Ó²úÆ·ÓÅ»¯µÄÇ÷ÊÆ£¬¾§ìͿƼ¼ÍƳöÖ§³Ö3.3V¹©µçµÄÒÔÏÂÐͺţºAZRS3072¡¢AZRS3076ºÍAZRS6023£¬ÈýÕßµÄÖ÷Òª²îÒìÔÚÓÚ×î¸ßÊý¾Ý´«ÊäËÙ¶È£¨AZRS3072Ö§³Ö×î¸ß250kbps£¬AZRS3076Ö§³Ö×î¸ß16Mbps£¬AZRS6023Ö§³Ö×î¸ß60Mbps£©¡£ÈýÕß²»½öÖ§³Ö¸üµÍ¹¦ºÄµÄ3.3V MCU£¬ÇÒÔÚͨÐÅʱÄÚ²¿·¢ËÍÆ÷µÄÊä³öµçÁ÷Ò²¸üµÍ£¨Ïàͬ½ÚµãÊýÁ¿¸ºÔØÏ£©¡£´ËÍ⣬ÈýÕß¶¼Ö§³ÖShutdownģʽ£¨ÐèÉèÖÃREB= Vcc, DE= 0£©£¬ÔÚShutdownģʽÏ£¬AZRS3072ºÍAZRS3076µÄ¹©µçµçÁ÷£¨ISHDN£©½öΪ10uA£¨Max.£©£¬AZRS6023½öΪ20uA£¨Max.£©¡£Shutdownģʽ¿ÉÒÔÅäºÏ¹¤³§ÖÇÄÜ»¯£¬¹Ø±Õ²»ÐèÒªµÄRS-485½Úµã£¬ÒÔ½µµÍ½Úµã¹¦ºÄ£¬ÓÅ»¯¹¤³§µÄ¹©µç¸ººÉ£¬ÂõÏòÖÇÄÜ»¯ÂÌÉ«¹¤³§¡£
ÔÚESD¾²µç·À»¤·½Ã棬ÈýÕß×ÜÏß¾ù´ïµ½IEC 61000-4-2 ±15kV£¨½Ó´¥£©/ ±18kV£¨¿ÕÆø£©Ë®Æ½£¬ÈçTable 2Ëùʾ¡£
| P/N | Max. Data Rate | Supply Current in Shutdown Mode (REB= Vcc, DE= 0) ISHDN |
IEC 61000-4-2 ESD for Bus (Contact/Air) |
||||||||
| AZRS3072 | 250kbps | 10uA | ±15kV/±18kV | ||||||||
| AZRS3076 | 16Mbps | 10uA | ±15kV/±18kV | ||||||||
| AZRS6023 | 60Mbps | 20uA | ±15kV/±18kV | ||||||||
Table 2. ¾ßÓÐShutdown¹¦ÄÜÇÒ3.3V¹©µçµÄRS-485
3. ¸ß¿É¿¿£¨¸ßESD/EOS·À»¤µÄRS-485):
¹¤³§µÄµç×ÓÉ豸ÈôÊܵ½ESD/EOSÄÜÁ¿³å»÷£¬½«µ¼ÖÂÉ豸²»Îȶ¨»ò¹ÊÕÏÒþ»¼¡£¾§ìͿƼ¼ÍƳö¸ßESD/EOS·À»¤µÄRS-485ÊÕ·¢Æ÷AZRS3082ºÍAZRS6534£¬¶þÕßµÄÖ÷Òª²îÒìÔÚÓÚ×î¸ßÊý¾Ý´«ÊäËÙ¶È£¨AZRS3082Ö§³Ö×î¸ß115kbps£¬AZRS6534Ö§³Ö×î¸ß8Mbps£©¡£¶þÕßÓÅÔ½µÄESD¡¢EFTºÍSurge¹æ¸ñÈçTable 3Ëùʾ¡£
| P/N | Max. Data Rate | IEC 61000-4-2 ESD for Bus (Contact/Air) |
IEC 61000-4-4 EFT for Bus |
IEC 61000-4-5 Surge for Bus |
| AZRS3082 | 115kbps | ±30kV/±30kV | ±4.4kV(5/50ns)* | ±30A(8/20us) |
| AZRS6534 | 8Mbps | ±30kV/±30kV | ±4.4kV(5/50ns) | ±30A(8/20us) |
*Note: In the IEC 61000-4-4 EFT ±4.4kV (5/50ns) waveform test, the current is approximately ±88A.
Table 3. ¸ßESD/EOS·À»¤µÄRS-485
×ÛÉÏËùÊö£¬ÎªÏìÓ¦Ã÷ÈÕ¹¤³§µÄÖÇ»ÛÉý¼¶£¬¾§ìͿƼ¼ÌṩÖÇÄÜ»¯[ÎÞ¼«ÐÔ£¨Polarity-Free£©]¡¢½ÚÄÜ£¨¾ßÓÐShutdown¹¦ÄÜÇÒ3.3V¹©µç£©¡¢¸ß¿É¿¿£¨¸ßESD/EOS·À»¤£©µÄRS-485ÊÕ·¢Æ÷¡£ÈçÓÐÏà¹ØÐèÇ󣬻¶ÓǢѯ¡£
Reference:
[1] https://zh.wikipedia.org/zh-tw/EIA-485




