Solution:

PenMount DOS driver only supports resolution 640x480 with 16 colors. Otherwise, under resolution 800x600 or higher, some applications work normally but some don't. This is because Penmount DOS driver can't simulate functions of all mosue drivers completely. To solve this problem, user have to understand the way to communicate with touchscreen controller and get controller messages directly via RS-232 port in higher resolutions video mode. The attached example program is for users to know method of communicating with touchscreen controller.