Interval timing routines for the IBM PC/XT/AT microcomputer family

We describe a 1-msec software timer for measuring response latencies and controlling delays on the IBM PC/XT/AT without additional hardware requirements. To demonstrate the machine language routines, a short BASIC example program is included. In a simple experimental design, two different stimulus words are presented on screen and keypress response latencies are measured. Precise timing of stimulus presentation is accomplished by direct manipulation of the video controller. The principles of programming interrupt-controlled timing routines are addressed to be easily adapted to other problems or different programming languages.