This Technical Note describes three problems with the Enhanced IIe ROMs and some suggested solutions.
The following three anomalies are known to occur when the Enhanced IIe ROMs are present:
Note: There is no way to display four lines of 40-column text at the bottom of the double high-resolution screen in mixed mode since the 80-column hardware must be active while double high-resolution graphics are being displayed.
To use the second method, however, does require some special considerations.
The Apple IIe scroll routine continues to use the window parameters when scrolling, but uses the 80COL soft switch to determine if it should scroll the 80- or 40-column screen. Since the firmware has initialized a 40-column window, the scroll routines will move only the first 40 columns. But, the 80COL flag has been turned on for double high-resolution, therefore, the scrolling routine takes every even column from auxiliary memory and every odd column from main memory. As a result, only the first 40 columns get scrolled, 20 columns from auxiliary memory and 20 columns from main memory.
One possible solution to the problem is to write your own scroll routines. Another might be to write to the screen so that scrolling will not occur. But there is yet another solution. Turn on the full 80-column mode with a PR#3 or the equivalent. Now print your text to COUT in the normal manner, being careful not to exceed 40 characters per line. The 80 column firmware will scroll everything properly. When you are ready to display text, send a Control-Q sequence through COUT to switch to 40 columns. When you are ready to return to double high-resolution mode, send a Control-R sequence to COUT.
When switching modes, a momentary glitch may occur. If you send the Control-Q sequence to COUT while still in graphics mode, the screen will go to regular single high-resolution mode before finally going to text mode. If you switch to text mode first, the text will be in 80-column mode (with 40 columns displayed on the left half of the screen) before ultimately going to 40-column mode. The same potential glitch may occur going back to double high-resolution mode. The glitch will be only momentary and may not present any problem for your application.
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