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#21
November 26th 04, 01:01 AM
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Motherboards are designed for numerous configurations. Some
configurations may want single point ground located elsewhere. Some configurations may attach the entire motherboard to chassis plate, and insulate chassis plate so that single point ground is between chassis plate and chassis. Furthermore, all mounting holes must be plated through. Computer assembler is expected to bring basic electrical knowledge to the assembly. He - not the motherboard manufacturer - decides where the single point ground will be made. Motherboard manufacture makes products with numerous options. Computer assembler decides how to implement those options. Cross talk and other problems are why computer boards are multi-layer assemblies using a copper plane for ground and other planes for Vcc. Same problems also why Intel (not the PC board designer) defines exact copper layout for PC traces to CPU. The layout is that critical. Electronic nature even of copper is but one reason why a CPU power supply is adjacent to the CPU and why newer ATX power supplies have a second power cable. Measure the conductivity between too ends of that motherboard ground plane. To meter, DC voltage is a perfect short. In reality, electric currents are RF electricity. No copper - even the ground plane - is a perfect conductor. All copper has significant impedance. Impedance (not resistance) is why Intel provides a layout for connections to their CPUs. Impedance is why bypass capacitors are scattered all over the motherboard. Conductors are electronic components when discussing RF currents to computers and in external generated transients. RF is why copper is not truly conductive. If copper were truly conductive, then antennas would not transmit and receive. Best antennas have near zero resistance and a specific impedance. The impedance (not resistance) makes multiple grounding of a motherboard problematic. Just another reason why grounds are at a single point. All conductors are electronic components. As Gary notes: ... at the frequencies modern computer systems operate at they have to use multiple grounds otherwise the systems become inoperable/unreliable because of cross talk. Problems are not just limited cross talk. Cross talk alone is not the reason for all those bypass capacitors. All PC traces and even the PC board ground plane are electronic components. Some currents (ie static electricity) through a ground plane can cause catastrophic consequences especially in hospital equipment. All grounds must be interconnected. So again, the interconnections between various grounds use the single point concept. Hospitals take the concept even one step farther. Hospitals do single point grounding on a room and on a building wide level. Bottom line for computer assemblers who learn new tricks - a single point connection between motherboard and chassis plate is best adjacent to IO slots and power connection. This post demonstrates another technical reason why: all conductors are electronic components; especially when dealing with RF frequencies in computers and in static electric discharges. Just another reason why more reliable computers uses the single point grounding technique. "We never did that before. Therefore we don't have to do that." People with this mentality need not reply. Unlike other posts that disagree, these posts technically explain why, provide examples, and provide experiments to demonstrate the problem. IOW these posts are based upon the science and not upon the myths so common among computer assemblers. These posts are for those who keep learning new techniques. Single point grounding of motherboard to chassis is the preferred mounting method. Provided here is but another reason why: RF currents make copper an electronic component. The relevant parameter is impedance. Gary wrote: I read the article and it mainly deals with analog devices and/or A/D converters and low frequency PIC chips. While it is true that multiple grounds can create ground loops creating hum in audio or telephone circuits we're dealing with radio frequencies in the hundreds of megahertz for the system bus / memory and in the gigahertz region in the case of the processor. What the article didn't address and is more of a concern to motherboard manufacturers is cross talk. One example of cross talk is noise from one set of data / memory lines at 100/133/400 megahertz bleeding over onto another set of data / memory lines. In computer circuitry this is disastrous. What may be a ground at DC or in low level audio or radio circuits can be a great antenna for radiating noise at 100+ megahertz. I'm an amateur radio licensee and I've got an antenna that's at DC ground potential. If you measured the resistance between the two leads to it, its a dead short and would be a short even up to the range of several megahertz. But if is a great antenna at 144 thru 148 Megahertz. ( Our 2 meter VHF band ) I've gone over this years ago with another person and I did a search and found a web site of a computerized medical equipment manufacturer ( not too much room for error there ) and they stated just what I have above and that is at the frequencies modern computer systems operate at they have to use multiple grounds otherwise the systems become inoperable/unreliable because of cross talk. The late 70's era Radio Shack Model 1's expansion interface was a classic example of cross talk. It was housed in a plastic case and radiated almost as much cross talk inducing noise as a radio station and was notoriously unstable. It only ran at around 1 megahertz if memory serves me correctly. You'd also have to ask yourself if motherboard manufacturers didn't want the motherboards to be grounded to the brass standoffs why do they conveniently put a couple of soldered circles right in the exact spot where those standoffs are ? As an experiment you can take and attach the power leads part way onto the motherboard ( so the tips of your ohmmeter can connect to the metal surfaces ), then take an ohmmeter and measure the resistance between those soldered circles and the ground wires and you'll find that it's a dead short, at least it was on any motherboard I've ever checked. HTH Gary 
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#22
November 26th 04, 03:01 AM
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In other words.
"If you can't dazzle them with brilliance, baffle them with bull****." Most of what w_tom writes has nothing to do with the subject. The rest is trolling. w_tom wrote: Path: newssvr11.news.prodigy.com!newscon03.news.prodigy. com!newsmst01a.news.prodigy.com!prodigy.com!border 1.nntp.dca.giganews.com!nntp.giganews.com!local1.n ntp.dca.giganews.com!nntp.nni.com!news.nni.com.POS TED!not-for-mail NNTP-Posting-Date: Thu, 25 Nov 2004 13:29:29 -0600 Message-ID: Date: Thu, 25 Nov 2004 14:23:24 -0500 From: w_tom X-Mailer: Mozilla 4.75 [en] (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 Newsgroups: alt.comp.hardware.pc-homebuilt Subject: Installing MoBo References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 68 NNTP-Posting-Host: 216.107.36.42 X-Trace: sv3-rGZv+Nu+UKw4I7TfjyHJBmBmaA+42whNUTXru7GqRNc2WwkrVa eNg4PHAGdi2o0V4jM6S7LRmW8G9q8!PB8WZHg7uhhVhR3GjfOA esFPi4Vo3vH0k6v9oKJTFdbZuhUM+YVen7Xc5CBCljU= X-Complaints-To: X-DMCA-Complaints-To: X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.20 Xref: newsmst01a.news.prodigy.com alt.comp.hardware.pc-homebuilt:422981 Static electricity to the chassis is not absorbed by a mythical chassis capacitance, and does not damage electronic components by passing through motherboard logic ground. Static electric discharge causes voltage differences in the ground plane resulting in digital ICs at different ground voltages. As even National Semiconductor app notes demonstrated (and NatSemi had some of the best databooks containing only application notes), ICs are most susceptible to erroneous operation when noise (that static electric discharge from a human) appears on IC's ground pin. PC board designs go to great lengths to minimize potential differences on ground plane. For example, 0.01 uf bypass capacitors are placed everywhere on motherboard board because voltage differences can exist and cause computer crashes. Proper grounding is so important (notice the many posters here that remain in denial) that a recent trade rag discusses grounding complexity: http://www.edn.com/toc-archive/2004/20041111.html But all this bypass capacitance and other PC board design techniques are for naught when transient currents enter ground plane on one side and leave on another. Solution is simple and well known - especially in high reliability designs. Logic (motherboard) ground makes a single point connection to chassis ground. A transient to chassis has only one incoming point and no outgoing point. Therefore no transient currents flow through motherboard - to cause computer crashes. Not computer damage. We are discussing noise that causes erroneous digital operation - crashes. Computer crash avoided because external transients (ie static electric discharge from human) do not pass through motherboard IF motherboard is mounted with a single point connection between logic ground and chassis ground. Bottom line - when motherboard is mounted with a single conductive connection to chassis ground, then motherboard is more resilient to external transients. This single point ground must be located adjacent to IO slots and power connector.
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#23
November 26th 04, 03:22 AM
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"JAD" wrote:
alt.computerhardware.science-PSU snore It's not that complicated. It goes something like this. .... The biggest maker of computer cases includes a lot of accessories but no insulating washers. .... Asus, Microstar International, and other mainboard makers include a lot of accessories but no insulating washers. .... Mainboards include solder coated electricity conductive rings on their mounting holes. .... Those mounting holes are connected directly to mainboard device ground pins. You can tell this by using a continuity checker or a simple ohm meter. .... All of the above circumstances lead to one conclusion. Computer assemblers and home computer builders are going to short mainboard device ground to the case. .... Neither case manufacturers nor mainboard manufacturers warn their customers about doing so. .... Taking into consideration all of the above facts, the conclusion is obvious (at least to me). .... Most modern mainboards are designed to be grounded to the computer case at their mounting holes. You can tell them by the fact that they have electricity conductive mounting holes. A conductor is there to conduct electricity, not to insulate something.
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#25
November 26th 04, 03:32 AM
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the only boards I have seen that had no ground rings and had traces
anywhere near the mounting holes was a 8086. "John Doe" wrote in message ... "JAD" wrote: alt.computerhardware.science-PSU snore It's not that complicated. It goes something like this. ... The biggest maker of computer cases includes a lot of accessories but no insulating washers. ... Asus, Microstar International, and other mainboard makers include a lot of accessories but no insulating washers. ... Mainboards include solder coated electricity conductive rings on their mounting holes. ... Those mounting holes are connected directly to mainboard device ground pins. You can tell this by using a continuity checker or a simple ohm meter. ... All of the above circumstances lead to one conclusion. Computer assemblers and home computer builders are going to short mainboard device ground to the case. ... Neither case manufacturers nor mainboard manufacturers warn their customers about doing so. ... Taking into consideration all of the above facts, the conclusion is obvious (at least to me). ... Most modern mainboards are designed to be grounded to the computer case at their mounting holes. You can tell them by the fact that they have electricity conductive mounting holes. A conductor is there to conduct electricity, not to insulate something.
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#26
November 26th 04, 04:13 AM
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"Martin G.1.0" wrote:
Don't listen to w_tom. It ain't easy. He is not here to help or discuss, but rather to abuse people as he has been doing for years. Just add him to your kill filters along with the other internet kooks as many others have done. He can bring out the best intelligent counter replies to his silliness, especially when the other author(s) does not know how silly w_tom is being. Hey, I need the education.
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#27
November 26th 04, 06:17 AM
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w_tom wrote:
Grounding concepts in that cited microchip discussion are same. No, they are not 'the same', and that you think they are belies your lack= =20 of understanding of it. Separate digital, analog, and other grounds with a single point connection is done for same reason that motherboard's logic ground is isolated from chassis ground.=20 Provided were examples, underlying technical concepts, and simple experiments that demonstrate the problem. What you 'provided' was a pile of B.S. Deny it all you want - without posting a single technical fact. I gave you, among other things, the reason for the separate analog ground= =20 and also explained the problem 'single point ground' has with frequencies= =20 over 1 Mhz, but, as usual, you snip out what you then claim wasn't given.= Intuitive reasoning without years of engineering training and experience means junk science reasoning. Describing yourself again, I see. But then, David, we have dealt with your junk science claims previously. I suppose that means you still haven't figured out that surge protection = which keeps every external connection to the computer at the same potenti= al=20 protects the internals. Without a technical reason why, the denial is only a 'junk science' response. You are the biggest purveyor of 'junk science' I've run across in a long = time, but you win the pompous A-hole category hands down. So that external transient currents do not pass through the logic ground (cause computer crashes), that logic ground must make only one connection to the chassis ground. Since you want to concentrate solely on 'external transients', an 'extern= al=20 transient' has only two ways to get into the computer. One would be throu= gh=20 the grounded case, an impossibility (if it's properly designed). The othe= r=20 is via an external device (or power) connection and what you want to do i= s=20 shunt that to case as soon as possible rather than have it traverse throu= gh=20 the whole system seeking your beloved 'single point ground'. Look up Intel 29835002.pdf, Intel=AE 815E Chipset Platform Design Guide, = section 2.2 Electrostatic Discharge Platform Recommendations where it=20 specifies connecting *two* motherboard mounting holes to ground, one on=20 each side of the rear I/O area, so that any ESD there is shunted to case = in=20 the shortest possible path. This single point grounding technique - done for same reasons to eliminate ground loops in stereo systems - makes a more reliable computer. 'Hum' in an audio system is not an external ESD transient nor is it above= 1=20 Mhz. It is, however, another example of how you take something completely= =20 unrelated and misapply it with your B.S. 'examples'. =20 David Maynard wrote: =20 That's a typical analog single point circuit ground, the primary purpos= e being to isolate the analog section from the digital section's switchin= g induced ground noise; which has nothing to do with chassis/motherboard shield grounding. It is intuitively obvious to even the most casual observer, however, that a 9.6 inch by 9.6 inch ground planed mATX motherboard does not=20 present a 'single point ground' to it's components. The point being,=20 while a 'single point ground' has specific uses, to then go dancing=20 around claiming it's 'the solution' to everything under the sun is to not understand it.
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#28
November 26th 04, 07:15 PM
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David Maynard provides an Intel example of the single point
ground technique. Intel recommends two screws at the far end of a motherboard so that, again, electrical currents in the chassis do not pass through motherboard logic ground. The single point ground, IO board connections, and power input connect to chassis at the same single point - at the far end of a motherboard. Where I recommended only one screw connection, Intel recommends two in the same location to create the single point ground at the farthest edge of motherboard. Demonstrated by page 30 of that Intel 815E Chipset Platform document, no currents across electronic sections of motherboard means no computer crashes due to static electric discharges to chassis. Best not to mount motherboard with conductive connections everywhere. Intel recommends only two connection, both at the far edge to make same single point ground - adjacent to IO slots and power connector. Intel document does not recommend conductive standoffs everywhere on motherboard - as I had posted. David Maynard wrote: ... Look up Intel 29835002.pdf, Intel® 815E Chipset Platform Design Guide, section 2.2 Electrostatic Discharge Platform Recommendations where it specifies connecting *two* motherboard mounting holes to ground, one on each side of the rear I/O area, so that any ESD there is shunted to case in the shortest possible path. ...
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#29
November 26th 04, 07:17 PM
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He cannot challenge the science, so his reasoning goes
something like this. The manufacturer does this and says nothing. Therefore the manufacturer expected you to do that. Scientific proof? Of course not. Reasoning based upon speculation. Its not complicated. If only a single point connection between motherboard' logic ground and chassis ground, then no transient currents in chassis ground will pass across logic ground to interfere with digital circuits. No transient currents through electronic area of motherboard means static electricity cannot crash the computer. Nothing new or complex here. We did this 30 years ago to make more reliable products. However it does contradict what many computer assemblers were told. Computer assemblers who never learned basic electrical concepts can have a problem with this superior motherboard mounting technique. They fear change. Some will even post insults because they so fear new techniques. Some will post "They did this; therefore they must have expected you to do that". Wild speculation does not create facts. Mount the motherboard with a single point ground. John Doe wrote: It's not that complicated. It goes something like this. ... The biggest maker of computer cases includes a lot of accessories but no insulating washers. ... Asus, Microstar International, and other mainboard makers include a lot of accessories but no insulating washers. ... Mainboards include solder coated electricity conductive rings on their mounting holes. ... Those mounting holes are connected directly to mainboard device ground pins. You can tell this by using a continuity checker or a simple ohm meter. ... All of the above circumstances lead to one conclusion. Computer assemblers and home computer builders are going to short mainboard device ground to the case. ... Neither case manufacturers nor mainboard manufacturers warn their customers about doing so. ... Taking into consideration all of the above facts, the conclusion is obvious (at least to me). ... Most modern mainboards are designed to be grounded to the computer case at their mounting holes. You can tell them by the fact that they have electricity conductive mounting holes. A conductor is there to conduct electricity, not to insulate something.
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#30
November 26th 04, 10:05 PM
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um if this is the case, what are MB manufactures trying to do? By
putting ground rings around each mount hole(on both sides in some cases), they are in fact saying this point needs to be grounded. If they did not want a ground point there, the ring should be non conductive. Makes little sense and To point out 1 single scenario on one particular board, and if it was DM stating it, knowing him he probably stayed up all night finding the one 1 single situation that supports whatever his point is. "w_tom" wrote in message ... David Maynard provides an Intel example of the single point ground technique. Intel recommends two screws at the far end of a motherboard so that, again, electrical currents in the chassis do not pass through motherboard logic ground. The single point ground, IO board connections, and power input connect to chassis at the same single point - at the far end of a motherboard. Where I recommended only one screw connection, Intel recommends two in the same location to create the single point ground at the farthest edge of motherboard. Demonstrated by page 30 of that Intel 815E Chipset Platform document, no currents across electronic sections of motherboard means no computer crashes due to static electric discharges to chassis. Best not to mount motherboard with conductive connections everywhere. Intel recommends only two connection, both at the far edge to make same single point ground - adjacent to IO slots and power connector. Intel document does not recommend conductive standoffs everywhere on motherboard - as I had posted. David Maynard wrote: ... Look up Intel 29835002.pdf, Intel® 815E Chipset Platform Design Guide, section 2.2 Electrostatic Discharge Platform Recommendations where it specifies connecting *two* motherboard mounting holes to ground, one on each side of the rear I/O area, so that any ESD there is shunted to case in the shortest possible path. ...
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