<![CDATA[#electronics people.]]> people. What is the point of doing this? Both inputs to this 74LS86 unit are high, but one has a 10K resistor on it.

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]]>https://board.circlewithadot.net/topic/902da804-5448-4d9a-a3e8-ab24ce3f7d44/electronics-people.RSS for NodeFri, 15 May 2026 03:40:36 GMTTue, 21 Apr 2026 19:10:53 GMT60<![CDATA[Reply to #electronics people. on Wed, 22 Apr 2026 02:01:05 GMT]]>@bytex64 @gloriouscow I do not think it makes sense but I always do it... (ok, alsmost always)

]]>https://board.circlewithadot.net/post/https://infosec.exchange/users/RueNahcMohr/statuses/116445889547792020https://board.circlewithadot.net/post/https://infosec.exchange/users/RueNahcMohr/statuses/116445889547792020Wed, 22 Apr 2026 02:01:05 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 21:59:22 GMT]]>@bytex64 @philcowans @gloriouscow right, doing this on my phone, so rather suboptimal conditions. I might have to wait until my morning for a full analysis, but the XOR output being indirectly involved in the 14MHz clock output, among other things, points me to some clock generator optimisation at startup. Possibly allowing the crystal to "wake up" faster as @bytex64 hinted at.
Lemme sleep on that 😴

]]>https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444939077121297https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444939077121297Tue, 21 Apr 2026 21:59:22 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 21:05:19 GMT]]>@gloriouscow @RueNahcMohr Well, now that I think about it that makes no sense. If it’s all tied to VCC it can’t be higher that VCC. ᖍ(ᐙ)ᖌ

]]>https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444726520574185https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444726520574185Tue, 21 Apr 2026 21:05:19 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 21:04:10 GMT]]>@philcowans @gloriouscow @jmrubillon Gloriouscow posted high res schematics recently, which is what started this whole adventure, I think. 🙂 https://archive.org/details/pcjr_schematics_4800dpi.7z

]]>https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444722032258790https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444722032258790Tue, 21 Apr 2026 21:04:10 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 21:01:47 GMT]]>@bytex64 @philcowans @gloriouscow I've tried finding the schematics to figure it out properly, but I haven't found those yet. Maybe someone could post a link to them here and we can all be better informed?

]]>https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444712616884865https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444712616884865Tue, 21 Apr 2026 21:01:47 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 20:52:56 GMT]]>Sorry for the incomplete circuit.

I think what you are all saying about an initial high pulse makes sense - the F/C input to the 8284 doesn't need a pulse, but this effectively suppresses the OSC clock output for a little bit, which probably helps stability as the motherboard starts up.

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]]>https://board.circlewithadot.net/post/https://oldbytes.space/users/gloriouscow/statuses/116444677857677382https://board.circlewithadot.net/post/https://oldbytes.space/users/gloriouscow/statuses/116444677857677382Tue, 21 Apr 2026 20:52:56 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 20:42:31 GMT]]>@philcowans @gloriouscow @jmrubillon Or it’s a debugging hack to allow clock injection. Pull down the input against the resistor to switch off the internal oscillator. But I’d expect a test point or something in that case.

]]>https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444636896502376https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444636896502376Tue, 21 Apr 2026 20:42:31 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 20:40:05 GMT]]>@gloriouscow To let the input be used by something in the future without PCB redesign ?

]]>https://board.circlewithadot.net/post/https://mstdn.social/users/Extelec/statuses/116444627315634779https://board.circlewithadot.net/post/https://mstdn.social/users/Extelec/statuses/116444627315634779Tue, 21 Apr 2026 20:40:05 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 20:38:50 GMT]]>@RueNahcMohr @gloriouscow I think maybe some chips can be damaged if the pin voltage is higher than VCC, which might happen on startup or if the signal crosses power domains. And the resistors limit damaging currents. But that’s mostly a guess on my part.

]]>https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444622395503579https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444622395503579Tue, 21 Apr 2026 20:38:50 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 20:35:11 GMT]]>@philcowans @gloriouscow @jmrubillon That is weird. Makes me wonder if it’s some deep voodoo magic to kickstart the oscillator or make it stabilize faster or something.

]]>https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444608030489183https://board.circlewithadot.net/post/https://awesome.garden/users/bytex64/statuses/116444608030489183Tue, 21 Apr 2026 20:35:11 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 20:13:42 GMT]]>@philcowans @gloriouscow in the absence of a more complete schematic, it's fairly difficult to say what exactly it's for. Based on past high volume designs, a reset pulse is a reasonable assumption. Now, if it's connected to a crystal, I'd have to see the rest of the circuit to say what it actually does.
But a pulse at power on is what this setup generates.

]]>https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444523535758266https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444523535758266Tue, 21 Apr 2026 20:13:42 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 19:31:03 GMT]]>@gloriouscow in my early digital days, I learned that it's bad to tie a digital line straight to vcc. Today I always use resistors. I do not know what conditions not having the resistor causes damage.

]]>https://board.circlewithadot.net/post/https://infosec.exchange/users/RueNahcMohr/statuses/116444355853601458https://board.circlewithadot.net/post/https://infosec.exchange/users/RueNahcMohr/statuses/116444355853601458Tue, 21 Apr 2026 19:31:03 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 19:26:27 GMT]]>@gloriouscow They want a glitch? I mean the parasitic capacitance of the trace will mean pin 1 changes a bit later than pin 2, so the output of the gate will be a very short pulse at power on.

]]>https://board.circlewithadot.net/post/https://chaos.social/users/ChuckMcManis/statuses/116444337746417916https://board.circlewithadot.net/post/https://chaos.social/users/ChuckMcManis/statuses/116444337746417916Tue, 21 Apr 2026 19:26:27 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 19:23:16 GMT]]>@gloriouscow power on reset. The 10k combined with the input's capacitance, forms a small delay, guaranteeing a pulse at power on.

]]>https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444325216789856https://board.circlewithadot.net/post/https://mastodon.ie/users/jmrubillon/statuses/116444325216789856Tue, 21 Apr 2026 19:23:16 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 19:18:54 GMT]]>@gloriouscow maybe something like ensuring a decisive behaviour during power up?

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/hannorein/statuses/116444308101584342https://board.circlewithadot.net/post/https://mastodon.social/users/hannorein/statuses/116444308101584342Tue, 21 Apr 2026 19:18:54 GMT<![CDATA[Reply to #electronics people. on Tue, 21 Apr 2026 19:17:04 GMT]]>@gloriouscow reset pulse at power up maybe?

]]>https://board.circlewithadot.net/post/https://mamot.fr/users/obstsalat/statuses/116444300887640479https://board.circlewithadot.net/post/https://mamot.fr/users/obstsalat/statuses/116444300887640479Tue, 21 Apr 2026 19:17:04 GMT