Is the provided RS485 terminal the GND or Shield?

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It may not display this or other websites correctly.<br />You should upgrade or use an <a href="https://www.google.com/chrome/" target="_blank" rel="noopener">alternative browser</a>.</div> <div class="p-body-header"> <div class="p-title "> <h1 class="p-title-value">Is the provided RS485 terminal the GND or Shield?</h1> </div> <div class="p-description"> <ul class="listInline listInline--bullet"> <li> <i class="fa--xf fal fa-user" aria-hidden="true" title="Thread starter"></i> <span class="u-srOnly">Thread starter</span> <a href="/members/cm64.614085/" class="username u-concealed" dir="auto" data-user-id="614085" data-xf-init="member-tooltip">cm64</a> </li> <li> <i class="fa--xf fal fa-clock" aria-hidden="true" title="Start date"></i> <span class="u-srOnly">Start date</span> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/" class="u-concealed"><time class="u-dt" dir="auto" datetime="2024-11-22T20:02:08+0000" data-time="1732305728" data-date-string="Nov 22, 2024" data-time-string="8:02 PM" title="Nov 22, 2024 at 8:02 PM">Yesterday at 8:02 PM</time></a> </li> </ul> </div> </div> <div class="p-body-main p-body-main--withSidebar "> <div class="p-body-contentCol"></div> <div class="p-body-sidebarCol"></div> <div class="p-body-content">  <div id='div-gpt-eda_wallpaper'> <script> googletag.cmd.push(function() { googletag.display('div-gpt-eda_wallpaper'); }); </script> </div> <div class="p-body-pageContent"> <div class="block block--messages " data-xf-init="lightbox select-to-quote" data-message-selector=".js-post" data-lb-id="thread-413114"> <div class="block-outer"></div> <div class="block-outer js-threadStatusField"></div> <div class="block-container"> <div class="block-body"> <article class="message message--post js-post js-inlineModContainer " data-author="cm64" data-content="post-1784407" id="js-post-1784407" > <span class="u-anchorTarget" id="post-1784407"></span> <div class="message-header"> <header class="message-attribution message-attribution--split"> <ul class="message-attribution-main listInline "> <li class="u-concealed"> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/post-1784407" rel="nofollow" > <time class="u-dt" dir="auto" datetime="2024-11-22T20:02:08+0000" data-time="1732305728" data-date-string="Nov 22, 2024" data-time-string="8:02 PM" title="Nov 22, 2024 at 8:02 PM">Yesterday at 8:02 PM</time> </a> </li> </ul> <ul class="message-attribution-opposite message-attribution-opposite--list "> <li> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/post-1784407" class="message-attribution-gadget" data-xf-init="share-tooltip" data-href="/posts/1784407/share" aria-label="Share" rel="nofollow"> <i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/post-1784407" rel="nofollow"> #1 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" > <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/cm64.614085/" class="avatar avatar--m avatar--default avatar--default--dynamic" data-user-id="614085" data-xf-init="member-tooltip" style="background-color: #5cd67a; color: #1a662d"> <span class="avatar-u614085-m" role="img" aria-label="cm64">C</span> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/cm64.614085/" class="username " dir="auto" data-user-id="614085" data-xf-init="member-tooltip">cm64</a></h4> <h5 class="userTitle message-userTitle" dir="auto">Newbie level 6</h5> </div> <img src="/styles/images/ranks/blevel3.gif" alt="Newbie level 6"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Jan 7, 2019</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>12</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/cm64.614085" class="fauxBlockLink-linkRow u-concealed">0</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>0</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 98 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784407" data-lb-caption-desc="cm64 · Nov 22, 2024 at 8:02 PM"> <article class="message-body js-selectToQuote"> <div > <div class="bbWrapper">Regarding an RS485 to TTL converter here: <a href="https://docs.m5stack.com/en/unit/iso485" target="_blank" class="link link--external" rel="nofollow ugc noopener">https://docs.m5stack.com/en/unit/iso485</a><br /> <br /> In ISO485 terminals it shows ground instead of shield as the third terminal as here <a href="https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_04.webp" target="_blank" class="link link--external" rel="nofollow ugc noopener">https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_04.webp</a> and here: <a href="https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_02.webp" target="_blank" class="link link--external" rel="nofollow ugc noopener">https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_02.webp</a><br /> <br /> But in the schematics it shows that terminal as shield: <a href="https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_sch_01.webp" target="_blank" class="link link--external" rel="nofollow ugc noopener">https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_sch_01.webp</a><br /> <br /> I guess it makes sense it is GND since it is RS485 requirements.<br /> <br /> So what is the GND terminal really connected to? Is it connected to the GND of RS485 side or the the node shown as shield in the schematics(where there is an RC parallel filter)?</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/reply?quote=1784407" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1784407/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> </div> </article> </div> </div> </div> <div class="block block--messages" data-xf-init="" data-type="post" data-href="/inline-mod/" data-search-target="*"> <span class="u-anchorTarget" id="posts"></span> 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<i class="fa--xf fal fa-share-alt" aria-hidden="true"></i> </a> </li> <li> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/post-1784417" rel="nofollow"> #2 </a> </li> </ul> </header> </div> <div class="message-inner"> <div class="message-cell message-cell--user"> <section class="message-user" itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/barry.35520/"> <meta itemprop="url" content="https://www.edaboard.com/members/barry.35520/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/barry.35520/" class="avatar avatar--m" data-user-id="35520" data-xf-init="member-tooltip"> <img src="/data/avatars/m/35/35520.jpg?1591248332" alt="barry" class="avatar-u35520-m" width="96" height="96" loading="lazy" itemprop="image" /> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/barry.35520/" class="username " dir="auto" data-user-id="35520" data-xf-init="member-tooltip"><span itemprop="name">barry</span></a></h4> <h5 class="userTitle message-userTitle" dir="auto" itemprop="jobTitle">Advanced Member level 7</h5> </div> <img src="/styles/images/ranks/hlevel4.gif" alt="Advanced Member level 7"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Mar 31, 2005</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>6,561</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>1,206</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/barry.35520" class="fauxBlockLink-linkRow u-concealed">2,424</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>1,435</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1,393</dd> </dl> <dl class="pairs pairs--justified locationBlock"> <dt>Location</dt> <dd> <a href="/misc/location-info?location=California%2C+USA" rel="nofollow noreferrer" target="_blank" class="u-concealed">California, USA</a> </dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 35,681 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784417" data-lb-caption-desc="barry · Nov 22, 2024 at 11:00 PM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">There is no "GROUND of RS485".</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set actionBar-set--external"> <a href="/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/reply?quote=1784417" class="actionBar-action actionBar-action--reply" title="Reply, quoting this message" rel="nofollow" data-xf-click="quote" data-quote-href="/posts/1784417/quote">Reply</a> </div> </div> <div class="reactionsBar js-reactionsList "> </div> <br/> <div class="js-historyTarget message-historyTarget toggleTarget" data-href="trigger-href"></div> </footer> </div> </div> <div class="message-cell message-cell--vote"> <div class="message-column"> <div class="contentVote js-contentVote " data-xf-init="content-vote" data-content-id="post-1784417"> <meta itemprop="upvoteCount" content="0" /> 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itemprop="author" itemscope itemtype="https://schema.org/Person" itemid="https://www.edaboard.com/members/klausst.544298/"> <meta itemprop="url" content="https://www.edaboard.com/members/klausst.544298/" /> <div class="message-avatar "> <div class="message-avatar-wrapper"> <a href="/members/klausst.544298/" class="avatar avatar--m" data-user-id="544298" data-xf-init="member-tooltip"> <img src="/data/avatars/m/544/544298.jpg?1591959018" srcset="/data/avatars/l/544/544298.jpg?1591959018 2x" alt="KlausST" class="avatar-u544298-m" width="96" height="96" loading="lazy" itemprop="image" /> </a> </div> </div> <div class="message-userDetails"> <h4 class="message-name"><a href="/members/klausst.544298/" class="username " dir="auto" data-user-id="544298" data-xf-init="member-tooltip"><span itemprop="name">KlausST</span></a></h4> <h5 class="userTitle message-userTitle" dir="auto" itemprop="jobTitle">Advanced Member level 7</h5> </div> <img src="/styles/images/ranks/hlevel4.gif" alt="Advanced Member level 7"> <div class="message-userExtras"> <dl class="pairs pairs--justified joinedBlock"> <dt>Joined</dt> <dd>Apr 17, 2014</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed"> <dt>Messages</dt> <dd>26,150</dd> </dl> <dl class="pairs pairs--justified"> <dt> Helped</dt> <dd>4,919</dd> </dl> <dl class="pairs pairs--justified"> <dt>Reputation </dt> <dd> <a href="/reputation/authors/klausst.544298" class="fauxBlockLink-linkRow u-concealed">9,863</a> </dd> </dl> <dl class="pairs pairs--justified"> <dt>Reaction score</dt> <dd>5,769</dd> </dl> <dl class="pairs pairs--justified pairs--xbBoxed trophyBlock"> <dt>Trophy points</dt> <dd>1,393</dd> </dl> <dl class="pairs pairs--justified creditBlock"> <dt title="Activity points">Activity points</dt> <dd> <a href="/activity/" data-xf-click="overlay" class="fauxBlockLink-blockLink u-concealed"> 175,784 </a> </dd> </dl> </div> <span class="message-userArrow"></span> </section> </div> <div class="message-cell message-cell--main"> <div class="message-main js-quickEditTarget"> <div class="message-content js-messageContent"> <div class="message-userContent lbContainer js-lbContainer " data-lb-id="post-1784426" data-lb-caption-desc="KlausST · Nov 23, 2024 at 2:23 AM"> <article class="message-body js-selectToQuote"> <div itemprop="text"> <div class="bbWrapper">Hi,<br /> <br /> RS485 is differential signalling. So theoretically it needs no GND... in the eaning of signal transmission.<br /> <br /> However, in most cases the receivers are semiconductors ... and those semiconductors have a limited and specified "common mode voltage range".<br /> This CMVR is given with respect to the receiver IC´s GND. <br /> This GND is a sytem_GND not necessarily EARTH_GND.<br /> <br /> On the transmitter side ... you also very often have semiconductors.<br /> They generate the differential RS485 signals. Generated by an IC ... which also refer´s to it´s IC_GND. (Again: not necessarily EARTH)<br /> The usual operational output voltage range of each single RS485 signal is within 0V to 5V referenced to it´s GND. <br /> <br /> So to ensure the reciever can work within it´s CMVR (which often is +/-7V wider than output voltage range --> -7V ... +12V) it is the eaysiest way to connect: [transmitter_GND] -- [cable_SHIELD] -- [receiver_GND].<br /> <br /> ****<br /> <br /> On the transmitter side ... it is allowed to connect the [transmitter_GND] -- [EARTH_GND]<br /> The same is true for the receiver side.<br /> <br /> Now in high power industrial designs with long distance between RS485 partners ... there will be unavoidable voltage shift (bounce) between these two EARTH potentials.<br /> --> to ensure proper operation ... the receivers have this +/-7V wider input voltage range. This allows "hard" potential shift between transmitter and receiver of up to +/-7V.<br /> <br /> ***<br /> <br /> When one or both partners are not connected to EARTH_GND .. the partners are considered "floating" to each other. Now when you connect two floting partners ... there will be a shift in potential. It may be in the kV range when ESD is invloved. Each partner will have some stray capacitance to EARTH_GND. So when connecting each other the potentials need to match .. thus there will be a short peak current. Starting with a rather high voltage difference ... and thus maybe high - but short - current peak.<br /> <br /> Now imagine the shields are not connected to their own´s IC´s GND .... then this equalizing current needs to flow through the signal lines.<br /> But you don´t want to flow ESD (machine to machine) currents to any signal lines. This would need rather big overvoltage protection.<br /> Here also the GND_connected shield helps. <br /> <br /> ***<br /> <br /> To make an industrial system more robust one often uses gavanically isolated RS485 signals .. and the according ICs.<br /> This has two major benefits. <br /> * the voltage shift between two partners (main circuit) can be way higher than +/-7V ... maybe some 100 volts. <br /> * the stray capacitance to GND will be much lower ... so the ESD energy is much lower, resulting in less stress for the ESD protection.e<br /> Using the word GND in the meaning of voltage reference there can be this GND system<br /> <br /> A side <--> B side<br /> [EARTH_GND_A] - isolated or not - [SYS_GND_A] - isolated or not - [RS485_GND_A] - usually connected via shield- [RS485_GND_B] - isolated or not - [SYS_GND_B] - isolated or not - [EARTH_GND_B]<br /> <br /> ** <br /> Looks more complicated than it is. It gives you a lot of freedom to use isolation or not. <br /> But in either case it is recommended to connect:<br /> [RS485_GND_A] - connected via shield- [RS485_GND_B]<br /> <br /> ***<br /> <br /> If for any reason you don´t want to hard connect the shields with the RS485_GND, then you need to use three resistors:<br /> (from a PROFIBUS recommendation)<br /> VCC - 390 Ohms - Signal B - 220 Ohms - Signal A - 390 Ohms GND<br /> This is termination and signal biasing combined (and adjusting common mode voltage range)<br /> <br /> <br /> Klaus</div> </div> <div class="js-selectToQuoteEnd"> </div> </article> </div> </div> <footer class="message-footer"> <div class="message-microdata" itemprop="interactionStatistic" itemtype="https://schema.org/InteractionCounter" itemscope> <meta itemprop="userInteractionCount" content="0" /> <meta itemprop="interactionType" content="https://schema.org/LikeAction" /> </div> <div class="message-actionBar actionBar"> <div class="actionBar-set 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Are you sure you want to submit this form?", attach: "Attach files", rich_text_box: "Rich text box", close: "Close", link_copied_to_clipboard: "Link copied to clipboard.", text_copied_to_clipboard: "Text copied to clipboard.", loading: "Loading…", you_have_exceeded_maximum_number_of_selectable_items: "You have exceeded the maximum number of selectable items.", processing: "Processing", 'processing...': "Processing…", showing_x_of_y_items: "Showing {count} of {total} items", showing_all_items: "Showing all items", no_items_to_display: "No items to display", number_button_up: "Increase", number_button_down: "Decrease", push_enable_notification_title: "Push notifications enabled successfully at Forum for Electronics", push_enable_notification_body: "Thank you for enabling push notifications!", pull_down_to_refresh: "Pull down to refresh", release_to_refresh: "Release to refresh", refreshing: "Refreshing…" , "svStandardLib_time.day": "{count} day", "svStandardLib_time.days": "{count} days", "svStandardLib_time.hour": "{count} hour", "svStandardLib_time.hours": "{count} hours", "svStandardLib_time.minute": "{count} minutes", "svStandardLib_time.minutes": "{count} minutes", "svStandardLib_time.month": "{count} month", "svStandardLib_time.months": "{count} months", "svStandardLib_time.second": "{count} second", "svStandardLib_time.seconds": "{count} seconds", "svStandardLib_time.week": "time.week", "svStandardLib_time.weeks": "{count} weeks", "svStandardLib_time.year": "{count} year", "svStandardLib_time.years": "{count} years" }); </script> <form style="display:none" hidden="hidden"> <input type="text" name="_xfClientLoadTime" value="" id="_xfClientLoadTime" title="_xfClientLoadTime" tabindex="-1" /> </form>  <script type="application/ld+json"> { "@context": "https://schema.org", "@type": "QAPage", "url": "https://www.edaboard.com/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/", "mainEntity": { "@type": "Question", "@id": "https://www.edaboard.com/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/", "name": "Is the provided RS485 terminal the GND or Shield?", "datePublished": "2024-11-22T20:02:08+00:00", "url": "https://www.edaboard.com/threads/is-the-provided-rs485-terminal-the-gnd-or-shield.413114/", "text": "Regarding an RS485 to TTL converter here: https://docs.m5stack.com/en/unit/iso485\n\nIn ISO485 terminals it shows ground instead of shield as the third terminal as here https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_04.webp and here: https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_02.webp\n\nBut in the schematics it shows that terminal as shield: https://static-cdn.m5stack.com/resource/docs/products/unit/iso485/iso485_sch_01.webp\n\nI guess it makes sense it is GND since it is RS485 requirements.\n\nSo what is the GND terminal really connected to? Is it connected to the GND of RS485 side or the the node shown as shield in the schematics(where there is an RC parallel filter)?", "answerCount": 2, "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/cm64.614085/", "name": "cm64", "url": "https://www.edaboard.com/members/cm64.614085/" }, "suggestedAnswer": [ { "@type": "Answer", "datePublished": "2024-11-23T02:23:57+00:00", "url": "https://www.edaboard.com/posts/1784426/", "text": "Hi,\n\nRS485 is differential signalling. So theoretically it needs no GND... in the eaning of signal transmission.\n\nHowever, in most cases the receivers are semiconductors ... and those semiconductors have a limited and specified \"common mode voltage range\".\nThis CMVR is given with respect to the receiver IC\u00b4s GND. \nThis GND is a sytem_GND not necessarily EARTH_GND.\n\nOn the transmitter side ... you also very often have semiconductors.\nThey generate the differential RS485 signals. Generated by an IC ... which also refer\u00b4s to it\u00b4s IC_GND. (Again: not necessarily EARTH)\nThe usual operational output voltage range of each single RS485 signal is within 0V to 5V referenced to it\u00b4s GND. \n\nSo to ensure the reciever can work within it\u00b4s CMVR (which often is +/-7V wider than output voltage range --> -7V ... +12V) it is the eaysiest way to connect: [transmitter_GND] -- [cable_SHIELD] -- [receiver_GND].\n\n****\n\nOn the transmitter side ... it is allowed to connect the [transmitter_GND] -- [EARTH_GND]\nThe same is true for the receiver side.\n\nNow in high power industrial designs with long distance between RS485 partners ... there will be unavoidable voltage shift (bounce) between these two EARTH potentials.\n--> to ensure proper operation ... the receivers have this +/-7V wider input voltage range. This allows \"hard\" potential shift between transmitter and receiver of up to +/-7V.\n\n***\n\nWhen one or both partners are not connected to EARTH_GND .. the partners are considered \"floating\" to each other. Now when you connect two floting partners ... there will be a shift in potential. It may be in the kV range when ESD is invloved. Each partner will have some stray capacitance to EARTH_GND. So when connecting each other the potentials need to match .. thus there will be a short peak current. Starting with a rather high voltage difference ... and thus maybe high - but short - current peak.\n\nNow imagine the shields are not connected to their own\u00b4s IC\u00b4s GND .... then this equalizing current needs to flow through the signal lines.\nBut you don\u00b4t want to flow ESD (machine to machine) currents to any signal lines. This would need rather big overvoltage protection.\nHere also the GND_connected shield helps. \n\n***\n\nTo make an industrial system more robust one often uses gavanically isolated RS485 signals .. and the according ICs.\nThis has two major benefits. \n* the voltage shift between two partners (main circuit) can be way higher than +/-7V ... maybe some 100 volts. \n* the stray capacitance to GND will be much lower ... so the ESD energy is much lower, resulting in less stress for the ESD protection.e\nUsing the word GND in the meaning of voltage reference there can be this GND system\n\nA side <--> B side\n[EARTH_GND_A] - isolated or not - [SYS_GND_A] - isolated or not - [RS485_GND_A] - usually connected via shield- [RS485_GND_B] - isolated or not - [SYS_GND_B] - isolated or not - [EARTH_GND_B]\n\n** \nLooks more complicated than it is. It gives you a lot of freedom to use isolation or not. \nBut in either case it is recommended to connect:\n[RS485_GND_A] - connected via shield- [RS485_GND_B]\n\n***\n\nIf for any reason you don\u00b4t want to hard connect the shields with the RS485_GND, then you need to use three resistors:\n(from a PROFIBUS recommendation)\nVCC - 390 Ohms - Signal B - 220 Ohms - Signal A - 390 Ohms GND\nThis is termination and signal biasing combined (and adjusting common mode voltage range)\n\n\nKlaus", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/klausst.544298/", "name": "KlausST", "url": "https://www.edaboard.com/members/klausst.544298/" } }, { "@type": "Answer", "datePublished": "2024-11-22T23:00:44+00:00", "url": "https://www.edaboard.com/posts/1784417/", "text": "There is no \"GROUND of RS485\".", "upvoteCount": 0, "author": { "@type": "Person", "@id": "https://www.edaboard.com/members/barry.35520/", "name": "barry", "url": "https://www.edaboard.com/members/barry.35520/" } } ] }, "publisher": { "@type": "Organization", "name": "Forum for Electronics", "description": "International Electronics Discussion Forum: EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals", "url": "https://www.edaboard.com" } } </script> <script> $(function(){ var notice = $('.xb-welcome-notice'); if(notice.length){ var cookie = XF.Cookie.get('hide_welcome_notice'); if(!cookie){ XF.Cookie.set('hide_welcome_notice', Date.now()); notice.show(); } else if ((Date.now() - cookie) > 8.64e+7){ XF.Cookie.set('hide_welcome_notice', Date.now()); notice.show(); } else { notice.hide(); } } }); </script> </div> </body> </html>

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Is the provided RS485 terminal the GND or Shield? | Forum for Electronics