Talk:PS/2 port

message: Yes, it really is true -- at least on some older motherboards, unplugging a PS/2 device while powered will occasionally at least semi-permanently break the motherboard, such as blowing a special fuse. -69.87.204.161 01:03, 19 March 2007 (UTC)
replies: text: Really? I've done it dozens of times and never ever had a single computer fail because of that. I have also plugged mice in the keyboard plug, and the other way around, and I'd swear they worked, but I'm not sure on that one. — isilanes (talk|contribs) 09:45, 12 March 2008 (UTC)
replies: text:  As stated, it was primarily on older systems. I had a friend who co-op’d at the school board ~1996 where he did it with an IBM system (which was probably a few years older than that) and burned out the motherboard. On the other hand, the PS/2 connector on my EPoX EP-4B2A2 from 2002 eventually developed a bad connection after a few years and the keyboard would cut in and out, so I ended up having to disconnect and reconnect the keyboard countless times while the system was on, without hurting it. If I was in Windows, what would usually happen is that the typematic rates would get reset and I would have to change them back, otherwise nothing bad happened. Synetech (talk) 19:03, 20 June 2011 (UTC)
replies: text:  I used to work on PS/2 keyboard and mouse firmware in the 1990s and never saw a damaged motherboard due to hot plugging. All motherboards and interfaces, going right back to the original IBM systems, included protection devices for static discharge into the pins, overcurrent limiting and wrong polarity. Obviously the protection devices could be damaged with purposeful abuse, e.g. a high negative voltage for a long time into the data lines could overload the protection diodes, but normal use would rarely damage the ports electrically. I did see one motherboard with a fusible protection device on the power line which would require replacement on significant over current. None of these issues would be likely to occur through normal hot plugin. However, some BIOS/hardware could lock out the PS/2 interface if bad signal sequences were received (I saw many times while debugging kbd/mouse firmware). This would have either been a hardware shift register wrong state issue or bad BIOS code or a BIOS protection mechanism, ignoring apparently dodgy signals to prevent rubbish input for the user. Maybe this is what is being referred to? However this was never a hardware issue and caused no damage, only requiring reboot of the host system. Lkingscott (talk) 06:59, 29 September 2022 (UTC)
thread_title:  Damage 

message: I corrected some spelling errors. jpoke89 (talk) 11:49, 22 November 2007 (UTC)
thread_title:  Spelling 

message: Care should be taken to avoid connecting a keyboard to a mouse port or vice versa.[citation needed]
That's BS.  Electrically they're the same.  They signal the same.  On all modern motherboards both ports even go to the same chip.  The data format is different, but you won't harm or break anything by plugging the wrong thing into the wrong port.  —Preceding unsigned comment added by 72.29.167.236 (talk) 19:22, 20 September 2008 (UTC)
thread_title:  Mouse in keyboard port and vice versa 

message: What was the connector used in the original IBM PC? Family Guy Guy (talk) 04:34, 19 November 2008 (UTC)
replies: text: The IBM XT used a DIN connector - that used a different set of Scan codes. See this if you are interested in some technical details. Megapixie (talk) 04:43, 19 November 2008 (UTC)

text: PC keyboards use the same 5-pin DIN connector as AT keyboards and the pinout is the same as well (although not all ATs supported the RESET signal any more). However, the data going over the interface is different, PC keyboards use 9 bit frames, whereas AT keyboards use 11 bits. Also, PC keyboards send scan codes in what later became known as scan code set 1 (the only set supported by these keyboards), whereas AT keyboards use scan code set 2 by default (and MF keyboard introduced yet another set 3). For compatibility purposes, the keyboard controller on the mainboard translates these interface scancodes into codes according to set 1 for IRQ 1 (INT 9). There are very few exceptions (including some "obscure" IBM machines) where the scancodes are not translated by the keyboard controller ("pass-through mode"). In these cases, AT keyboards will have to be forced into scan code set 1 or the INT 9 interrupt handler of the keyboard driver will have to translate the codes itself. Scan code set 3 was meant to be used by PS/2 machines, but it is rarely used. While all MF keyboards supported all three scan code sets in the early 1990s, later low-quality keyboards were "optimized" to only support scan code set 2.--Matthiaspaul (talk) 01:26, 23 January 2012 (UTC)
thread_title:  Pre PC/AT Connector? 

message: CN means "it may be that this claim is true, but no reliable, published sources were given to verify it and the information is not considered common knowledge". That is a direct quote from the template description. It goes on to say that the template should be used "when there is a general question of the verifiability of a statement, or when an editor believes that a reference verifying the statement should be provided." 
This is why I insist on a CN tag for your "most." You see, the CN tag does not mean "I claim it's not true." It does not even mean "I'm doubtful about this." (There is a "doubtful" tag for that.) I'm saying it's not self-evident the way "the sky is blue" is, nor common knowledge like "the moon orbits the Earth" is, so by WP:V it needs to be cited. And the survey you did two years ago, while providing sufficient motivation for the inclusion of the claim, is not something that we can use as a citation nor sufficient to remove the CN tag. 
If I thought the "most motherboards" claim wasn't true I'd have used a "doubtful" tag instead. That validity of the claim is not what this dispute is about. The fact that it lacks a citation is. Jeh (talk) 08:36, 6 February 2013 (UTC)
replies: text: You seem to be so caught up in bureaucracy that you ignore the meaning of your own words. Reliable. Published. Verifiable. These words have meanings, and had them long before random internet denizens on Wikipedia wrote up articles on them. The information I have provided is reliable, it is published, and it is verifiable (although I can only assume you have not taken the time to verify it). I won’t again go into how WP:V does not trump other policies, but I will say I don’t see why you bother taking a position no dictionary editor would. It may not be self-evident the way claiming “the sky is blue” is, but it is self-evident all the same, and if you don’t see that, you have just been ignoring me this entire time. My survey might not be enough for you, but it is for me. :) As far as I can tell, it is not your clear distinction between  and , but your stubborn inability to accept reality over bureaucracy that motivates you. The validity is the only thing that matters. It is valid, and I wish you’d accept that; and that despite the myriad of Wikipedia bylaws, there is not an appropriate paper to push in every single situation. ¦ Reisio (talk) 01:14, 7 February 2013 (UTC)
thread_title:  CN vs. "doubtful" tags 

message: IMHO this wire color table should be removed completely. There are no standards or conventions for these things in the kinds of places where cheap commodity consumer goods (like computer keyboards) are made. This is just confusing to people who come here and need that kind of information most.  The very presence of multiple combinations should be a clue that this isn't really any kind of reliable information. At best, it is a collection of random anecdotes. If people want to know which color is which signal, they should be instructed to verify the pin assignments on the connector. That is the ONLY place that is guaranteed to be correct. Even the silk screen nomenclature on the PC board internal to the keyboard has been known to be incorrect. Rcrowley7 (talk) 20:07, 21 September 2010 (UTC)
replies: text: I agree. Be bold. ⇌Elektron 23:55, 30 January 2011 (UTC)
thread_title:  Color code 

message: Both use 5V DC, how can there be different voltage through an adapter? Zac67 (talk) 19:35, 26 May 2011 (UTC)
replies: text: On a motherboard I have next to me the 5v of both connect to the same point.  The ground is the main system ground.--Tagno25 (talk) 04:41, 1 October 2011 (UTC)

text: Both use 5V for power supply (although the original IBM PC apparently used 6V instead for its DIN keyboard interface), but the voltage levels for the data lines are different. The PS/2 interface uses 5V CMOS logic levels, whereas the USB data lines work at a much lower voltage level (however, they are 5V safe as well). PS/2-USB-adapters do not contain any electronics, they are passive adapters using a "tricky" wiring allowing the keyboard to detect if it is connected to a PS/2 port or not. If not, the controller in the keyboard will switch protocols (if the keyboard's firmware has been programmed to support both protocols), thereby giving the illusion of the adapter translating between PS/2 and USB protocols. Of course, this does not work, if the keyboard supports USB only. The PS/2 data lines are pulled up to 5V on the mainboard, but I don't see how this could become a problem because the USB data lines are 5V-safe as per the USB specification, and the keyboard must be designed to withstand this voltage on the data lines. --Matthiaspaul (talk) 00:32, 23 January 2012 (UTC)
replies: text: Thanks for clarifying, I was 'huh'-ing over this one. It could be made clearer in the article - I'll go do this in a min :) ☭ cmn ☭ ( ❝❞ /✍ ) 15:43, 8 April 2012 (UTC)
thread_title:  PS/2 & USB - different voltages? 

message: I’ve noticed that newer motherboards tend to have a single combined (half-green, half-purple) PS/2 port instead of separate ones. I’ve read conflicting information on what exactly they are for. Some people say that they make you choose either a PS/2 keyboard or a PS/2 mouse and have to use a USB one of the other, while (more) people say that you can use a PS/2 splitter (like the kind that laptop users sometimes use) to plug both devices into the dual-port. Motherboard manuals seem to vague or even lacking in their discussion of the combo-port.
It would be good if someone with a definitive answer could add it to the article. Synetech (talk) 19:03, 20 June 2011 (UTC)
replies: text: Splitters work by connecting one device as normal and connecting the other to the two spare pins (not sure which is which offhand). It would be down to the individual motherboard manufacturers whether they actually implement those two extra pins. So you aren't going to get a definitive answer only a "it works/doesn't work with board x" answerPlugwash (talk) 04:15, 16 January 2012 (UTC)
thread_title:  Combo-port 

message: There's note, that windows input driver v.8 no longer supports PS/2, but this topic Input and HID - Architecture and Driver Support shows the opposite.  — Preceding unsigned comment added by Bigbes (talk • contribs) 10:56, 31 December 2011 (UTC)
thread_title:  Microsoft driver 

message: I seem to remember that the legacy I/O devices take up valuable IRQs. A floppy, a COM port, a Keyboard socket and a mouse socket will take one interrupt each. Several devices can be attached to one USB bus and only take up one interrupt, although they may not perform as fast eg when using a keyboard for gaming.  — Preceding unsigned comment added by 92.26.151.41 (talk) 23:23, 22 January 2012 (UTC)
replies: text: Since the full support of PCIbus, APICs, etc., IRQs are no longer "valuable" anyway. Shared interrupts are expected and fully supported on PCI and PCI Express. Jeh (talk) 02:47, 30 January 2013 (UTC)
thread_title:  Interrupts 

message: I have a Deltaco external hard disk case, and its DC connector is just similar to PS/2, I tested it and a mouse connector fits perfectly. This article has nothing to say about power cable usage. 85.217.42.90 (talk) 17:09, 8 September 2013 (UTC)
replies: text: And it should not. What you're talking about is the physical connector type, which is a six-pin Mini-DIN connector. This article describes one use of such a connector. Similarly we have an article on D-subminiature connectors, and we have articles on Serial port and RS-232, but the latter two do not mention the many other ways 9- and 25-pin D-sub connectors are used. (Not to my recollection - if they do, that should be fixed too.) Jeh (talk) 17:44, 8 September 2013 (UTC)
replies: text: Sorry, I thought this was the main article. Didn't realize PS/2 is one of many. 85.217.42.90 (talk) 00:16, 9 September 2013 (UTC)
replies: text:  No problem at all, you pointed out something that IMO should be fixed by renaming this article. Btw I too have a few external HD enclosures with the six-pin mini-DIN power connectors... And I have a few others with a connector that looks identical... but look close and you see there are four thick pins instead of six slender ones. Far better for a power connector, and much more rugged, but nonstandard. Jeh (talk) 17:04, 9 September 2013 (UTC)
thread_title:  PS/2 power connector? 

message: Anent the above, this article is not so much about the physical connector (which, as the IP above pointed out, is used for other things, even in this exact configuration, the standard 6-pin type). It is about the signals and protocols and pinout that appear on the connector in this particular usage. Note that the articles on Serial port and RS-232 are not called "Serial connector" or "RS-232 connector". 
Accordingly, I think this article would be better named "PS/2 port".  I so propose. Please discuss. Jeh (talk) 17:44, 8 September 2013 (UTC)
replies: text: You might be right on this. 85.217.42.90 (talk) 00:17, 9 September 2013 (UTC)

text: Agree. Rename and add either a disambig or a redirect -- Akb4 (talk) 04:35, 5 December 2013 (UTC)

text: Well then, you should be happy, as there is already a redirect from PS/2 connector to PS/2 port, just as there is for Serial connector to Serial port. Jeh (talk) 22:59, 15 September 2014 (UTC)
thread_title:  Proposed move to "PS/2 port" 

message: The article notes that a number of peripherals were shipped with a chipset smart enough to detect whether it was plugged into a ps/2 port or a usb port and could auto-switch between the two, and that such devices generally had usb connectors on them, plus a passive usb to ps/2 adaptor. Is the reverse ever true? Are there devices that have an auto-detecting chipset and a ps/2 plug on them and a passive connector with a ps/2 socket and a usb plug? And are these passive connectors, either usb-plug-becomes-ps/2 plug or ps/2-plug-becomes-usb-plug (if those exist) interchangeable, or is there more than one possible pinout? -- Akb4 (talk) 04:35, 5 December 2013 (UTC)
thread_title:  usb over ps/2? 

message: I read this as hearsay all the time over the internet and I am perplexed because it simply can't be a hard rule.  The USB keyboard I use myself, Microsoft Sidewinder X4, manages to get around this mythical limit somehow, and it isn't simply due to their special keyboard software because it retains its ability to recognize like 15 keys at once in Linux as well.
Furthermore the "source" used to back this statement up is a link to another wiki.174.45.212.205 (talk) 01:36, 1 February 2014 (UTC)
thread_title:  USB 6-key limit 

message: In the "port availability" section:
> PS/2 mouse and keyboard connectors have also been used in non-IBM PC-compatible computer systems,
This reads as (non-IBM) (PC-compatible computer systems), when in fact it is trying to say (non-(IBM PC)-compatible) (computer systems).
96.50.85.160 (talk) 20:18, 8 April 2014 (UTC)
replies: text: WP:SOFIXIT. Since you spotted the problem, you can probably come up with a wording that fixes it. Jeh (talk) 20:38, 8 April 2014 (UTC)
thread_title:  non-PC use of PS/2 connector 

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thread_title:  External links modified 

message: In the Communication Protocol section, it says "To send a byte of data back to the keyboard, the computer pulls Clock low, waits briefly, then toggles it with a clock signal generated by the computer, while outputting a frame of bits on the Data line, one bit per Clock pulse, (...). The computer releases the Clock line when it is done.".
Does this imply that the host generates the clock while in host-to-device transmission?
Other sources [1][2][3][4] say that the device is always responsible for generating the clock cycle. When the host wants to transmit, it first pulls the CLOCK low to inhibit the transmission from the device, then it pulls DATA low, releases CLOCK and waits for the device to start generating the clock pulse.
[1] https://www.avrfreaks.net/sites/default/files/PS2%20Keyboard.pdf
[2] http://www.networktechinc.com/ps2-prots.html
[3] http://www.mcamafia.de/pdf/ibm_hitrc07.pdf
[4] https://web.archive.org/web/20180830070412/http://retired.beyondlogic.org/keyboard/keybrd.htm
Obs.: References [3] and [4] are included as references for this article.
I don't know if it is the case, but maybe the host is responsible for generating the clock on an older PS/2 protocol that I am not aware of? If not then the text should be corrected.  — Preceding unsigned comment added by 2A00:1398:4:3601:D37B:883D:9C3E:8857 (talk) 21:38, 28 December 2020 (UTC)
replies: text: I completely agree, I've rewritten the text. AFAIK, both AT and PS/2 have always had the device generate the clock. In any case, this is the usual mode, and if there are exceptions they should be called out explicitly. By the way, while I love Beyond Logic, that source ([4]) seems to have a mistake as it says  whereas the other three sources all agree that on host-to-device transmission, data is clocked in on rising edges instead. Digital Brains (talk) 11:31, 17 January 2021 (UTC)
thread_title:  Does the host generate the clock while in host-to-device transmission? 

message: When I came across this article I was surprised by the statement that motherboards still commonly include a PS2 port. I checked and as of 2022 this is correct, however as this is date relevant and the ports will most likely disappear or become less common at some point in the future then the statement will then no longer be true. Therefore I have added a date when this is known to be true. This should be updated in the future if the interface continues to be fitted to motherboards. Lkingscott (talk) 07:32, 29 September 2022 (UTC)
thread_title:  Add 2022 date when referring to continued availability