Posted By
gerliczer
on 2016-09-15
12:41:30
|  Re: Hey I've had a N.O.S plus/4 and about to show it off at a club at school
@Papa_Bear
There are usually two problems with running PAL programs on NTSC machines.
First, these machines can be switched between the two TV systems by setting one single bit in a specific control register of the video IC. The programming practice was simply ignoring this potential incompatibility source. And it is mostly still the same, which makes specific people grumble a bit. So, when you start programs that ignore that difference, you will often get a garbled screen. More so, because in reality it is not enough to set that bit only, an additional component must also be replaced to achieve actual compatibility with the selected TV system.
Second, if a PAL program makes operations long enough that they not finish before the display frame end occurs in an NTSC machine, it may lead to screen control falling out of synchrony with the screen refresh. PAL system has 312 display lines time between two frame ends, while NTSC system has 262 display lines between two frame ends. One line's time may be considered equal in both systems for our purpose. This means that there is 16% less time in an NTSC machine to finish all operations before refreshing the display than in a PAL machine. This may result in screen update glitches.
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