Copyfault
Registered: Dec 2001
Posts: 478 |
Concerning PAL-NTSC-Differences: exact amount of available cycles per second
Don't know if this is the right forum to ask this, but I'll give it a try...
I'm wondering about the exact amount of cycles per second on a PAL machine compared to a NTSC machine. Up to now, my simple approach was as follows:
PAL-TV-Norm: 625 interlaced lines/frame, 50Hz
PAL-C64: 312 frames (=floor(625/2))
63 cycles per rasterline (no badline, no sprites)
20 cycles per rasterline (badline, no sprites)
-> total number of cycles per second (standard PAL-screen with badlines, no sprites) =
(no.of nonbadlines*cycles + no.of badlines*cycles)*no.of frames per second =
((312-25)*63 + 25*20)*50 = (287*63 + 25*20)*50 = (18081 + 500)*50 = 18581*50 = 929050 cycles/second
NTSC-TV-Norm: 525 interlaced lines/frame, 60Hz
NTSC-C64: 262 frames (=floor(525/2))
65 cylces per rasterline (no bl, no spr)
22 cylces on a badline (no spr)
-> total number of cycles per second (standard NTSC-screen with badlines, no sprites) =
(no.of nonbadlines*cycles + no.of badlines*cycles)*no.of frames per second =
((262-25)*65 + 25*22)*60 = (237*65 + 25*22)*60 = (15405 + 550)*60 = 15955*60 = 957300 cycles/second
However, I found different values on the internet. For example, AAY64 has a table with the following values:
+----------+--------+-------+---------+---------+---------+------------+
| VIC | Video | # of | Cycles/ | Cycles/ | Frames/ | System |
| Type | system | lines | line | frame | second | Clock (Hz) | +----------+--------+-------+---------+---------+---------+------------+
| 6569 | PAL-B | 312 | 63 | 19656 | 50.125 | 985248 |
| 6567R8 | NTSC-M | 263 | 65 | 17095 | 59.826 | 1022727 |
+----------+--------+-------+---------+---------+---------+------------+
While it is clear that my calculations take bl into consideration while the other values don't, I'm stuck with the following questions:
i. How does it come that there are 263 rasterlines on an NTSC-machine, while the TV-Standard is 525 interlaced lines which should give 525/2 = 262.5 -> 262 (just like the math would be in PAL world)?
ii. Is the no. of frames/second really as stated in the table? Does it mean that the 51st PAL-frame is already started before the end of the respective second? And for NTSC, that the 60th frame is not fully finished?
Every hint's welcome! |
