Timing experiments need different types of input devices. The PXL programs currently support up to three different ways for response collection:
1. Input from the aviation control panel. This is the default if speed is not important or if many UTC different input signals are required.
2. Input from a timing control board that is connected to a parallel input port. On IBM PC compatible machines the parallel printer connector may be used to connect up to five digital input lines to the computer. The game port also contains 4 digital input switches. This type of input is very fast and allows for precise response timing.
3. Input from a mouse pointer and its buttons. Mouse devices usually have two or three buttons that may be used as response switches in a way comparable to special switchboards.
4. Selection of one of these timing input devices is done by setting the experimental variable switchtype to a numerical code that describes the device. Table scode contains the currently valid code values. The default is switchtype 0 which enables keyboard input. Code values from 1 to 19 are reserved for switchboard devices. Values from 1 to 5 are reserved for switchboards connected to the game port connector. Values from 11 to 16 are used by switches connected to one of the parallel printer connectors.
5. Thus switchtype timing has two functions: it tells Timing programs about the type of response device available, and it allows the user to select one device if several are available and the program is able to use different devices. Most programs are able to use any of the three devices possible. In these cases the variable switchtype may be used to tell the respective program which type of switch should be used. Note that the command line option may also be used to set the default input device. As described in other chapters, an assignment in a program's parameter file overrides the defaults. In some cases it is not sufficient to set the input device. It may also be necessary to tell a program the exact input codes in order to decide what are correct and false responses. An example is the program rtm. This gives the input codes for the switches of switch boards. The input codes for keyboard input are the corresponding ASCII values or the keyboard scan codes.
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