PS/2 or USB

[JudgeRob]

Does it matter?  Do the interfaces perform the same?  Lag?

Thanks,
JudgeRob

[Dal1980]

I'm no expert but there are restrictions on USB over PS/2 type. I think it's better to have PS/2 as it can handle more communication over USB. I heard about this on an arcade builders YouTube video about a couple of years ago. I wish I could be more specific than that but I seem to remember something like:

If you pressed 5 buttons together on a PS/2 type connection then there would be no problem however the USB type connection would not register 5 buttons simultaneously but I don't think any of this is relevant if you use controller cards anyway, the guy I was watching probably was talking about making his own hacked controller using an old keyboard and he probably recommended a PS/2 type for this reason. I think proper controllers don't have much of a problem as they a built specifically to handle a certain number of controls and you just buy 2 controller cards to handle 2 sets.

Sorry for the 'loose' information.

[PL1]

The 6-buton limitation that Dal1980 is referring to is imposed by "boot protocol".
(BYOAC search is your friend if you want to read more on the subject.)

No modern USB keyboard-style arcade encoders use boot protocol.

The only way you are likely to encounter it is with a keyboard hack or the old (pre-Feb 2014) version of the X-Arcade encoder.


Scott

[JudgeRob]

OK, thanks.  I was more curious if there was any slight lag issues with one compared to the other or some other weird limitation I hadn't heard of. 

[PL1]

OK, thanks.  I was more curious if there was any slight lag issues with one compared to the other or some other weird limitation I hadn't heard of.

You won't have any lag issues with encoders from any of the commonly-recommended vendors on BYOAC.

Some encoders that have been recently mentioned as possibly having lag issues are a few of the direct-from-china knockoff Xin-Mo's, but IIRC those claims were not confirmed. (The Xin-Mo's sold by GGG and Paradise do not suffer from lag AFAIK)

For most of us, the difference between PS/2 and USB is like the difference between an Average Joe trying to hit a 100 MPH fast ball vs. trying to hit a 95 MPH fast ball -- theoretically there is a 5% difference, but the practical outcome is indistinguishable.

As far as other encoder quirks to be aware of:
- X-Arcade encoder uses isolated grounds, one per connector (i.e. touch the 3rd input wire from connector A to the ground of connector B and it registers as the 3rd input wire of connector B)
- IIRC the GGG KeyWiz resets to the default keymap when you reboot -- requires software to re-load your custom keymap during bootup. (Not sure if this is still accurate since it appears that Randy has made some changes to the KeyWiz/software.   )


Scott

[adder]

usb.

ps2 is outdated, un-advantageous, unnecessary.

[RandyT]

ps2 is outdated, un-advantageous, unnecessary.

Not exactly.  PS/2 is a pure FIFO serial protocol.  If you have multiple players, and two players press a button nearly at the same time (i.e. within the USB report period) PS/2 will have a much better chance of actually registering which player got in first.  USB uses packetized information, and there is no standard which dictates how the information is acted upon when the packet is disassembled at the host.

For things like fighting games, quiz show type "buzzers" and other applications where you are really concerned about activation order, PS/2 is probably the way to go.  It also has virtually no limitation on the number of simultaneous button presses, depending on the interface.

I prefer PS/2, as it has worked perfectly for me for over a decade of playing.  I don't buy systems which don't have that port available, if it's for an arcade machine.  But USB keyboard interfaces can be be good too, if it's done well, the target OS supports it properly (some methods can be a problem with older OSes) and/or one works within the interfaces' limitations.

[DaOld Man]

If you have multiple players, and two players press a button nearly at the same time (i.e. within the USB report period) PS/2 will have a much better chance of actually registering which player got in first. 

I have a new excuse.

[AndyWarne]

usb.

ps2 is outdated, un-advantageous, unnecessary.

Correct.

Modern hardware and Windows version dont support PS/2 well, compared to USB.

I might have mentioned this before on here but a couple of years ago I was involved in a project in the processing center in the UK which deals with 75 of the UKs cheques (checks).
They have a room full of operators who key the check details from images presented on the screen. They upgraded all their PCs from an old model to new Dell units and kept the PS/2 numeric keypads. These were working fine on the older PCs but on the new ones they simply could not keep up with the keying rate of the operators.

We did some investigation and the problem was the way in which the PS/2 ports were implemented in hardware, sharing with the power control logic, and also the way in Which later Windows versions no longer directly read the ports but poll a buffer in the same way as USB does, only slower.

In the end the only solution was to replace all the numeric pads with new USB ones.

The fighting games argument works both ways because in these games, actions of individual presses are different to actions of simultaneous presses so any serial interface is going to have problems signalling a simultaneous press time and the slower the interface the more trouble it will have.

In the past this debate has raged on, so I will state now, that this is going to be my only post on this thread.

[RandyT]

Dells will be Dells.  This anecdotal evidence is not a valid argument against PS/2.  For a while, Dell implemented proprietary PS/2 hardware, causing even standard third-party keyboards not to function properly, and that decision to bind people to using Dell keyboards was the root of those issues.  They wised up (mostly) after the compatibility issues arose.

There is, however, a cost-cutting trend in some new, entry-level systems to use a controller chipset which is USB only, and which provides PS/2 support through the same technology as the PS/2 to USB adapters.  These are not true PS/2 ports, and it's easy to spot them by going into the device manager.  If all you see there is USB hardware, and no PS/2 ports, then there is no true PS/2 hardware present on the machine.  In our application, older, less expensive (often free) machines with older OSes and true PS/2 ports are more than capable, and used much more often than the latest Win10 machines. 

Windows obviously reads a buffer for both types of hardware.  The difference is the manner in which the data is collected, and the order it is read.  PS/2 uses a hardware FIFO buffer and it is still done the way it has always been done, via the BIOS.  And we aren't talking about "simultaneous" activations, as obviously in that case it falls down to collection order at the processor level, and precedence will necessarily need to be given to one or the other.  This is as close to a "wash" as is possible.  But when activation order is separated by less than the USB polling period, which is longer than the input polling period of any good interface, all of those events are presented to the host in the same packet, usually in random order, and the host has no idea which of those events happened first.  PS/2 is strictly serial processing, whereas USB data can be processed in parallel.

And using the word "slow" in this context is misleading.  Average human response time to a visual stimulus is about 250ms.  In that amount of time, PS/2 can process about 125 keystrokes/button events.  It's many, many times faster than is necessary for "real-time" human control.

As for it being "un-advantageous and unnecessary", a simple question arises.  Why then, is PS/2 functionality still included and touted as a feature on certain interface products?  From some of the posts I have seen on these boards, it seems to be there to use when the USB doesn't work correctly on certain OSes and/or system hardware, as the suggestion to correct these issues is more often than not to "use PS/2, if you can."