An odd support question that we receive occasionally is “I connected a Cedrus response pad to my computer and now the mouse cursor is moving by itself!”.

When this happens, it’s always a combination of two things:

• It’s a Windows computer, and,
• The response pad is using what we call the E-Prime protocol.

Other than our own RB response pad users, I think this blog post would be helpful to users of the original PST SRB and Chronos running in SRB emulation mode.

Background

The Cedrus RB Series response pads were designed to be universal and work with as many software packages as possible. To make them work with E-Prime, the response pads emulate PST’s older response device, the Serial Response Box (SRB) model 200A. The SRB works by sending the status of the keys to the computer about 800 times per second – regardless of whether a key is pressed or not.

The SRB sent its data to the computer via a serial port. It worked as intended.

So, What Happened?

In 2001, Microsoft released Windows XP with an interesting feature: when starting up, XP would scan all the COM ports (serial ports) to see if anything is connected. Microsoft wanted to simplify computer setup for users. Unfortunately, Windows XP would mistake the constant data coming from the SRB for a “Microsoft Serial Mouse”. This had two effects:

• The crazy mouse syndrome, with the mouse cursor acquiring a mind of its own, and,
• E-Prime was no longer able to use the response pad because it was now locked for exclusive use by Windows.

The workaround was simple enough: wait until Windows XP finished starting up before turning on the SRB (or the Cedrus response pad using the E-Prime / SRB protocol).

Things got worse with the release of Windows 7. That version was now scanning all COM ports seemingly all the time. Waiting to turn the response pad on was no longer helping.

Solution

The only solution we know of is to prevent Windows from scanning the COM ports. We found this helpful page:

‍        Disabling Windows detection of Serial Mice to fix “COM Port not available” errors

If you have not edited the Windows registry before (I haven’t), you might need assistance from your IT team. Cedrus cannot assist with this.

If You Own an Original SRB

A little known fact is that SuperLab supports input from the PST Serial Response Box. If you are considering moving away from E-Prime, you do not have to throw away your investment in hardware. You also gain platform independence: SuperLab supports the SRB on both Windows and Macintosh.

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