These are theoretical maximum heights,, and do not take into account any limitations of you! television or monitor. To be safe, 56 lines should be subtracted, giving the actual working screen height. For example:
E> Screen Open 0,320,Display Height-56,16,Lowres Print Display Height
Screen updating and running speeds
It is obviously impossible to slow down an NTSC television, just for the benefit of AMOS
Professional! If you want your programs to work at the same speed in either mode, special
action has to be taken. Look at this routine:
E> For T=0 To 60*50
Wait Vbl
Next T
Accounting for the difference in updating speeds, that last example delays a program for exactly one minute in PAL, but for only 50 seconds under NTSC. This is because the WAIT VBL command halts the program for one fiftieth of a second on a PAL machine, but for only one sixtieth of a second for NTSC.
Because NTSC machines are faster, all AMOS Professional programs will speed up dramatically when PAL versions are executed. Obviously this works the other way round as well, slowing down NTSC programs when run under the PAL system.
Also, AMAL will run more quickly under NTSC, and there will be a noticeable increase in the speed of animation sequences.
The good news is that music speed is not affected by these alternative modes. The bad news is that synchronised audio-visual sequences may well become out of step!
Even worse, what used to be a smoothly animated PAL display is likely to be transformed into a jerky NTSC animation, that stops at random intervals. The cause of this is almost certainly the fact that you are using loops for animation, graphic drawing, joystick tests, and so on, and that you assume they will be completed at each turn of the loop. However, if there is only one sixtieth of a second to execute the entire procedure instead of one fiftieth, the routine is overrunning its allotted time. This forces AMOS Professional to wait for the next VBL, throwing your entire sequence out of synchronisation.
To cure such synchronisation problems, you must ensure that all routines can be accomplished within the sixtieth of a second limit. This will guarantee that your program can run under either system, albeit at slightly different speeds.
If you are moving Objects directly from AMOS Professional Basic, you should try using AMAL for extra speed. Furthermore, if there are many Bobs on screen, replace the smaller, faster Bobs with Sprites, and be prepared for some encouraging results!