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Why is mouse jerky and what is the difference between PS/2 and a serial mouse?

Posted By : of Data Doctors on July 14, 1999

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I have a two-fold question. First, when I start the computer, about 75% of the time the mouse acts kind of freaky. You just touch it and the pointer moves all over the screen randomly opening and closing windows. In order to use the computer I have to reboot and disconnect the mouse, and then reconnect it when WIN95 gives the message about not detecting the mouse. It then works fine. I had checked in device manager and found that it showed both a serial and PS/2 mouse connected. I deleted the PS/2 mouse (obviously I'm using a serial mouse). This worked once but then the same problem reappeared. What is causing this???

Next, I figured maybe if I just change to a PS/2 mouse the problem will solve itself. I installed the PS/2 jack to the motherboard, disconnected the serial mouse and used the same mouse with a serial to PS/2 adapter from Belkin. Windows could not find the PS/2 mouse but will run the serial mouse after the mouse not found message appears.

Will the installation of the PS/2 mouse solve the jerky mouse pointer problem desribed above, and if so, how do I install the PS/2 mouse??

I appreciate your time and answer.


Rick T

aka [email protected]

This question was answered on July 14, 1999. Much of the information contained herein may have changed since posting.

Problem 1) The mouse is stuttering, sticking or moving in a jerky fashion

Explanation: The mouse's motion is not smooth and fluid the way it used to be or the way it should be When you move the mouse it tends to jump around or stutter, stops moving unless you shake it, or moves in a jerky fashion (the pointer seems to pause between redraws on the screen for example)

Diagnosis: There are four main causes of this sort of behavior The first is a dirty mouse, which can cause spurious behavior in a number of ways The second is a resource conflict with another device The third is damage to the mouse cord caused by excessive bending of the cord, especially near where it attaches to the mouse The fourth is a problem with the mouse driver, although this is much less likely.


Check the mouse to make sure that it is not physically sticking Clean the mouse

Try using a mouse pad instead of your desk (or other surface) for rolling the mouse In many cases the surface the mouse is on is actually the problem Using a mouse pad allows the mouse to roll smoothly (I have, however, seen desks that worked better without one.)

There may be a resource conflict, especially with regard to an IRQ channel This is especially true of serial mice, because of the fact that serial COM port pairs 1 and 3, and 2 and 4, share IRQ lines See here for more on resource conflicts regarding serial ports

Check the mouse cord to see if it is frayed or becoming loose If you see cracks in the plastic housing of the cord, this is a sign that this may be your problem If you have a soldering iron and patience, you can fix the problem, but replacing the mouse is normally the action of choice here

There may be a bad driver associated with this mouse It is unlikely that this is the case (since mice are such simple affairs) but is it possible


Problem 2) The problem is that the PS/2-style mouse and the serial mouse are not just different in terms of the connectors they use, they are different electrically as well The signaling levels are different, so just using an adapter will not always work What complicates the matter so much is that there are some mice that are called "combo" mice, which will automatically use either the PS/2 or the serial signaling depending on what sort of system they are plugged into This type of mouse, when used with an adapter of the sort mentioned above, will work in a serial port However, not all PS/2-style mice are combo mice, and this is what causes all the confusion To make matters worse, most mice do not have printed on them whether they are "combo" or not, and sometimes even the documentation is not very helpful (Buying a mouse with a PS/2 port that comes with a PS/2-to-serial adapter is a good hint that it is combo, of course!)


Check the instructions that come with your mouse to find out if it is a combo mouse If it is, then it should work with the adapter Make sure the adapter is tightly fitted to the connector and that there are no bent pins or other physical issues If the problem persists, troubleshoot the mouse more generally here

If you don't have a real combo mouse, or aren't sure if you do or not, then try borrowing one from another PC and see if it works instead If it does, then your mouse probably isn't a combo and you will need to purchase another that is (or just purchase a straight serial mouse, really, if that is what you want) If the other mouse doesn't work, then you either borrowed another one that isn't a combo, or you need to troubleshoot your mouse setup more generally

Hope this information will solve your problem, Good Luck!!

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Posted by of Data Doctors on July 14, 1999

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