LISTING SYSTEM

摘要

A control selectively sets flag bits in thos attribute codes corresponding to character boxes identified by the contents of a current location counter. A start point counter and end point counter determine that a point identified by the contents of the current location counter is coincident with the area of the rectangular box and is specified as an intersection point by the key entry device. A display is responsive to the flags to show on the screen vertical and horizontal grid lines passing through the intersection point within the rectangular box.