The Z80's secret feature discovered after 40 years! - Page 1
Forum section: electronics / general

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 16, 2022, 06:45:30 pm
content: Just happened to watch this a couple hours ago. Guess we get some similar suggestions.Note that (as almost always with YT videos), the title is a clickbait. There is no secret feature discovered after 40 years.

author: tggzzz
author_rank: Super Contributor
timestamp: October 16, 2022, 07:11:48 pm
content: Yet another example why I avoid yootoob vids.Remind me never to look at another vid you suggest.

author: MikeK
author_rank: Super Contributor
timestamp: October 16, 2022, 07:22:40 pm
content: Just how old is the video author?...Why would a child know anything secret about the Z80? More like their typical M.O. ...lie and brag.

author: DiTBho
author_rank: Super Contributor
timestamp: October 16, 2022, 07:43:02 pm
content: Quote from: tggzzz on October 16, 2022, 07:11:48 pmYouTube ... Clickbait. Well, that's depressing

author: DiTBho
author_rank: Super Contributor
timestamp: October 16, 2022, 07:44:09 pm
content: Ania commented "YouTube is not science"

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 16, 2022, 07:52:04 pm
content: Well, not to say that the video is not interesting though. Just that the title is a clickbait.Problem is, YT *does* promote those clickbait titles. That's how it works. If, as a youtuber, you don't follow the "rules", your channel will go down the drain.Blame YT, but not only. Blame the masses of viewers who consistently fall for that.

author: Tom45
author_rank: Frequent Contributor
timestamp: October 16, 2022, 08:03:04 pm
content: I recently watched a video on the Russian Mig-31.In the video he said that he included "Intercepting the SR-71" in the video's title to attract more viewers.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 16, 2022, 08:03:09 pm
content: Not a clickbait title, it's a lying title.To spare others' time, no Z80 secret feature was discovered. He wants to emulate protected mode in software, after adding some external hardware, then starts to fantasize about generic advantages of protected mode as if Z80 would have such a mode, except Z80 doesn't have any hidden protected mode feature.

author: tggzzz
author_rank: Super Contributor
timestamp: October 16, 2022, 08:25:34 pm
content: Quote from: RoGeorge on October 16, 2022, 08:03:09 pmYup.The ignoramus also made a comment that you couldn't have a preemptive operating system without protected mode.Oh yes you can, and on a Z80 too.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 19, 2022, 12:12:32 pm
content: Yeesh ok so bad call, I got clickbaited!

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 19, 2022, 12:37:27 pm
content: And it took you three days to realize it

author: TomS_
author_rank: Frequent Contributor
timestamp: October 20, 2022, 08:15:37 pm
content: I despise such videos/tactics and avoid them, and only watched this due to a few others I know commenting about it.But if you watch to the end he does at least admit that the title is click bait.But of course, you have to watch essentially the entire video to get to that point, which means feeding the algorithm.It's a neat trick, but certainly *not* a Z80 "feature".

author: M0HZH
author_rank: Regular Contributor
timestamp: October 20, 2022, 09:07:20 pm
content: Quote from: SiliconWizard on October 16, 2022, 07:52:04 pmThere are tons of channels that don't use clickbait and are very succesful, probably they know some sort of secret recipe like actually creating valuable content, who knows.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 28, 2022, 11:11:29 pm
content: Really? Please show us "very successful" YT channels that don't use those gross marketing techniques. They all do, and that's because that's how it works. There's no way around it. That's digital marketing. Sure some may be more subtle about it than others, but they still use the same techniques. That doesn't mean they have bad content. Even with the best of contents, you need this adapted marketing. If you don't like it, don't be on YT. And there can be a fine line between lies, exaggerations and overstatements. That's marketing in all its glory.Oh, and while I was even the first here to point out the clickbaity title, I'm pretty amazed about the reactions that some people had in this thread about this video. Good lord. Yes the title was a clickbait, yes the guy made a few gross overstatements in his video, but it was still not a bad video per se, it was not uninteresting, and it was kind of entertaining if you like vintage stuff and the Z80 in particular.So I don't think it has gotten a fair treatment here. Reporting it? Wow. Leaving a comment would have been enough.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 28, 2022, 11:52:23 pm
content: Any of the Brady Haran's YT channels?

author: Phil_G
author_rank: Regular Contributor
timestamp: October 29, 2022, 12:13:29 am
content: Quote from: SiliconWizard on October 28, 2022, 11:11:29 pmI think you're doing many Youtube contributors a disservice by making the common assumption that everyone who runs a YT channel does it to make money. The less greedy among us just find it a convenient video platform. There are many YT channels which I would consider 'very successful' in achieving their intent, without making a penny. I dont care a jot how the algorithm rates my own vids because none of the content is monetized. I dont care how many likes or views or subscribers I get. Surely you'd agree that YT has practical value, beyond the financial? Many enthusiasts use YT as a vlog or diary platform. To say that successful (adjective, accomplishing a desired aim or result) Youtube contributors "must use gross marketing techniques", "they all do" and "theres no way around it" and that otherwise "your channel will go down the drain" is not universally true..Sorry for the rant but it disappoints me that avarice is considered normal and to be expectedCheersPhil

author: amyk
author_rank: Super Contributor
timestamp: October 29, 2022, 06:18:51 am
content: When I saw the title I thought it was an analysis of the "trap gates"...https://retrocomputing.stackexchange.com/questions/11143/in-the-original-z80-layout-where-are-the-traps-located-and-what-are-their-ef

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 08:50:54 am
content: Quote from: amyk on October 29, 2022, 06:18:51 amDidn't know that, thanks!The pdf linked in the stackexchange reply:https://www.cl.cam.ac.uk/~sps32/Z80proj/Z80_traps.pdf

author: wraper
author_rank: Unknown
timestamp: October 29, 2022, 08:54:12 am
content: More secret features that will make you cringe

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 29, 2022, 09:21:48 am
content: Quote from: wraper on October 29, 2022, 08:54:12 am

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 09:45:07 am
content: Maybe the word "features" doesn't fit there, I'll read that rather as "tricks".Though, using copper wire makes a better soldering tip than any other material. With time, copper will dissolve in solder, but it's virtually free to replace it with another piece of wire. It will solder better than any monocartridge $50/piece top brands soldering tips. Also, shaping a copper wire to desolder many points at once works very well, too, often better than a desoldering station. Seems like good and practical tricks to me, subscribed, thanks!

author: wraper
author_rank: Unknown
timestamp: October 29, 2022, 10:01:37 am
content: Quote from: RoGeorge on October 29, 2022, 09:45:07 amMaking a tip which cannot touch the joint, and forces you to apply solder to the tip, not joint. Will beat any $5 soldering iron at sucking at doing its job. Tip does not fit shape of the hole, thus heater will have local overheating and heat transfer will be poor. Not to say original tip was made out of copper too with some thin plating. The only somewhat useful trick was with lighter (if you don't have soldering iron) but you don't need to flatten the solder. Many of those "secret features" may look nice on a first glance, but most of them are just useless garbage or totally fake.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 10:39:33 am
content: I agree, the soldering techniques might not be the best ones. The first solder looks better than the "recommended" second one, then later I think I've spotted a cold joint, applying soldering to the tip might make sense only when desoldering, and so on, but anyways, the tricks shown in that channel seemed more practical than the usual life-hacks videos I've seen before, that's why I clicked subscribe, for the hacks, not for soldering advice.About the copper wire as a soldering tip, in my experience plain copper was always better than any coated soldering tips. And they give peace of mind about not mixing Pb and Pb free, they don't need special re-tinning paste once in while, no need to religiously put fresh solder on a tip at the end of a soldering session, and so on.- Particularly well suited for heavy soldering on big joints or ground planes.- Could be used as an improvised micro soldering tip, too, by coiling a few turns of thin copper (AWG24, stripped from LAN cables) on a thick, plain-copper tip.That's how I've soldered this:without a $1k+ JBC micro soldering station.

author: wraper
author_rank: Unknown
timestamp: October 29, 2022, 10:54:18 am
content: Those cheap tips are just copper (or brass if total garbage) with a thin nickel plating, or something like that. So you need to grind that plating off for it to attract copper. Not like that plating will last long anyway. Not a proper iron plated copper tip all decent soldering irons have.QuoteThen just put a copper rod of appropriate diameter instead of original tip, not that folded garbage.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 04:12:32 pm
content: You are right again, a copper rod works even better.First thing I do after fitting a new folded wire is to snip it in half. Then twist the two parts together. A proper diameter copper rod might be hard to find, while thick solid copper is easy to get. I use leftovers from mains wiring.For example, this Z80 system I designed in the late 80s was soldered using twisted copper wire as a soldering tip, and a very powerful soldering gun of (100-200W and no temperature control):https://hackaday.io/project/1411-xor-hobby-a-vintage-z80-computer-prototypeThe wrapping wire was soldered instead of wrapped, and that type of wire was covered in something that couldn't stand the hit, so I've start soldering "through" the plastic, without stripping or even cutting the wire. Not exactly the best soldering practices. Though, last time I've powered it, it was still working. That was about 30+ years later after soldering through the cover of unstripped wrapping wire.It was stupid, but it works.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 29, 2022, 08:09:27 pm
content: Definitley, you don't need $1K equimement, it's a lot more the skill than the machine.When I was younger and poorer I only had the typical 30W unregulated pen-style JBC soldering iron. Yet I soldered a ton of tqfp and all kind of small stuff.This is an old picture on the OpenWRt forum, made by me.Wanted USB, the router didn't have, but the soc did. So I had to become creative.Why the scratching? Well, the AR9331 uses a weird package (Dual-row LPCC whatever) where one row will be hidden under the package.Pins on each row are separated by 0.5mm, then both rows are routed together to the top layer, so those wires are 0.25mm apart from each other!

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 08:31:14 pm
content: That's very hardcore!

author: wraper
author_rank: Unknown
timestamp: October 29, 2022, 08:44:52 pm
content: Watch this pron. In Russian but video shows it all. A 8 minutes you can see spiderweb.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 09:08:14 pm
content: Wow!

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 29, 2022, 09:37:28 pm
content: Someone had a lot of free time!What the hell happened to that card? Got ran-over by a train?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2022, 10:30:51 pm
content: I guess a short circuit in the original voltage stabilizer heated to hot red and carbonized the PCB.Or maybe the board was shot by a bullet.

author: wraper
author_rank: Unknown
timestamp: October 30, 2022, 08:59:44 am
content: Faulty buck converter burned the PCB. Someone removed PCB material before he received this board. He joked that it was given to beavers for fixing.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 30, 2022, 09:13:59 am
content: He was lucky to have the pcb files, otherwise it'd be unfixable.

author: wraper
author_rank: Unknown
timestamp: October 30, 2022, 09:20:56 am
content: Quote from: DavidAlfa on October 30, 2022, 09:13:59 amHe had a boardview for a similar board but not this one. So needed to figure out where traces by going over components/pads with copper braid to find continuity.

author: radiolistener
author_rank: Super Contributor
timestamp: November 24, 2023, 04:08:54 pm
content: Z80 really has some secrets which are discovered after 40 years, this is how some instructions affecting undocumented flags. Z80 has internal register which is updated on some instructions and undocumented flags are set depending on that hidden register.

author: iMo
author_rank: Super Contributor
timestamp: November 24, 2023, 06:05:50 pm
content: Those "hidden features/instructions" in the chips from 70/80ties are remnants of the design/testing/verification practices from that era. The focus was on the intended functionality only, their tools were simple (pencil and paper), they worked under time stress, etc., and when something toggled somewhere on the chip without an impact on the given specification they did not care much about it.A complete test of all the stuff on the chip is not possible even today..

author: radiolistener
author_rank: Super Contributor
timestamp: November 26, 2023, 01:28:56 pm
content: Quote from: iMo on November 24, 2023, 06:05:50 pmDo you know some feature of Z80 which is not implemented in modern emulators (which implements latest finding on MEMPTR register and all other undocumented features)?As I know Z80 die were scanned layer-by-layer on electronic microscope, it's schematic was reverse engineered and all its undocumented features were explained.There are several clones of Z80 with a little different behavior, for example OUT (C),0 can lead to write #FF on some clones.Here is picture of Z80 die:https://s.zeptobars.com/z80-Z0840004PSC-HD.jpgHere is some details on how its registers are implemented:https://www.righto.com/2014/10/how-z80s-registers-are-implemented-down.htmlWhat secret is still not reversed is FD1793. As I know some attempts to reverse engineering were made, it has some firmware inside. But there is still no full emulators for that chip. Here is a die photo of Russian clone 1818ВГ93:https://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/Kr1818vg93-3-HD.jpg/800px-Kr1818vg93-3-HD.jpgYou can identify internal ROM with firmware on the left top side. But I never seen that firmware content and it's description on internet. If someone have it, please let me know.

author: MarkT
author_rank: Frequent Contributor
timestamp: December 10, 2023, 11:59:15 am
content: I thought the fairly well known obscure undocumented Z80 feature was that the two bytes of the IX and IY registers can be addressed individually like HL by adding DD or FD prefix before H and L referencing opcodes, or something like that - basically the DD and FD prefixes just alter the meaning of "HL", "H" and "L". Never thought to try DD FD as a prefix though, suspect the last one wins.Whoops, still able to remember many Z80 opcodes decades after programming it. I blame the Sargon chess book that had a machine-code listing you could enter into your Z80 system of choice!! Still have the MOSTEK Z80 manual somewhere...