| 摘要 |
The described embodiment provides listing control on a cathode ray tube (CRT) display for simultaneously drawing horizontal and vertical grid lines within a square box displayed on the CRT screen by moving a cursor to the intersection point of these grid lines and by pressing an ENTER key. The embodiment uses a current position counter, a starting point counter and ending point counter to selectively set flag bits for horizontal and vertical grid lines stored in a logical page buffer so that the horizontal and vertical grid lines passing through the intersection point can be simultaneously displayed on the CRT screen. The embodiment uses the counters to define two end points on a diagonal line of the square box and to define the intersection point within the square box, whereby the flag bits are selectively set in accordance with the contents of these counters.
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