![]() ![]() ![]() Let's do one more calculation to complete the picture! This seems to be right with what we read about the system clock rates on Commodore C64 NTSC and PAL machines.Ĭongratulations! You are now able explain why the C64 has a certain system clock rate and that one period of this rate corresponds to a CPU Cycle which is the time required to put 8 pixels to the screen. One CPU-cycle corresponds therefor to 1/8 of the Dot Clock. This limits it to display 8 Pixels per each CPU cycle. ![]() So we have come from the Color Clock to the Dot Clock and the final destination would be the System Clock which defines a CPU Cycle. Nowadays it is not a problem anymore as HDMI and 60HZ are standard for TVs and supported by all current generation consoles. PAL system owners wanted to play the latest US-Games when they were released and not wait for adapted versions released 6+ months later. This explains why there were so many PAL-Fixes for games across systems in the old days. The common approach for commercial games was to create two versions of a product for NTSC and PAL markets though. Luckily many demos and a few games make sure they detect the underlying system correctly and change routines and timing in the code respectively. on Nintendo 64 ran 16% slower than the NTSC version of the same game on a US or Japanese Console - the reason is sloppy work on adapting to the PAL standard.īack to the C64. Interesting enough, while you would assume that this is a problem of the past, I want to remind you that many videogame console titles from Japan or the US where often not satisfactory adapted for the PAL market. That is especially notable when comparing many SID musics composed on one machine but played back on the other, e.g. This difference between PAL and NTSC systems leads to the problem that certain routines written for a PAL C64 may run 20% faster on a NTSC system while NTSC routines seem to be 16% slower on PAL. The properties of the C64 screen and the respective color standards lead to the required Dot Clock Rate which the Oscillator will generate for us. It is just simple math of the numbers of raster lines multiplied by the system refresh rate multiplied by the number of available pixels per each row. Of course you wonder what a Dot Clock is.Ī Dot Clock defines how many pixels can be drawn on the screen per each refresh. So that's the Color Clock.Īn integrated C64 circuit called a Dual Voltage Controlled Oscillator further generate a 7.88MHz (PAL) respectively 8.18MHz (NTSC) Dot Clock from this signal. Those frequencies are responsible how colors are displayed on our each TV systems. Do those numbers eventually ring a bell already?ģ.58Mhz is the color subcarrier frequency for the NTSC system while 4.43MHz corresponds to the color subcarrier frequency for PAL. Why Color Clock? Why did Commodore use crystals which generate exactly either of those two frequencies? When you divide 14.31818 by 4 you get 3.579545 and when you divide 17.734475 by 4 it results in 4.433618. ![]()
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