The optional number-of-lines is a numeric expression rounded to an integer and must be nine or greater. The bottom number-of-lines of the CRT are reserved for the alpha display. This can be useful in reserving the top of the CRT for the display of graphics. This command is equivalent to a CONTROL CRT,13;lines. If the number-of-lines is not specified, it is reset to the default.
If you are using SEPARATE ALPHA FROM GRAPHICS, you must specify when and where a pen-number that intersects with the alpha write enable mask. For example, on a 256 color display, the mask is 192 when SEPARATE. If pen-numbers of 0 to 7 are used, they won't intersect the mask and no alpha text will be written.
