VGA on Compact CRT? — #4

Post #4 by Bunsen

Source Forum	68kMLA
Category	Hardware
Post Date	Sat, 28 Nov 2009 - 20:34
Original URL	https://68kmla.org/bb/threads/vga-on-compact-crt.19126/

Post

Thoughts on TV (PAL/NTSC video):

(Much cutting and pasting from wikipedia)

The term PAL is often used informally to refer to a 625-line/50 Hz (576i), television system, and to differentiate from a 525-line/60 Hz (480i) NTSC system. / The line count and frame rate are defined as EIA 525/60 or CCIR 625/50. PAL and NTSC are only the method of the colour transmission used.

There may be errors, inaccuracies or approximations here:

Code:

Spec             unit         |   Mac       PAL       x       NTSC     x     |
==============================================================================
Clock frequency  MHz          |   15.6672   ?                 ?              |
Resolution:  H   pixels       |  512        n/a*                             |
         :  V   lines/frame  |  342        576i      1.68    480i     1.40  |
                lines/field  |             288       0.84    240      0.70  |
Scan Rate :  H   kHz          |   22.3       15.625   0.7      15.75   0.7   |
         :  V   Hz           |   60         50i      0.83     59.97  ~1     |
                Hz           |              25       0.42     29.94   0.5   |
==============================================================================

? even applicable?

* not applicable:

Analogue television signals have no pixels; they are rastered in scan lines, but along each line the signal is continuous.

i = interlaced ie alternating fields scanning alternate lines. Two fields per frame.

[PAL has] 575 scan lines of picture content / Also in analogue, 50 additional blank lines for the synch pulse are added, resulting in 625 lines.
When 576i is used / the odd field of the frame is transmitted first. This is the opposite of NTSC.

while NTSC has a total of 525 lines, only 480 of these are used to display the image for DV-NTSC. For analog NTSC there are 486 lines, and two of those 486 being half-lines (scan line number 263 which appears as the last scan line in the first (odd) field, and scan line number 283 which is the first scan line of the second (even) field; there are 525 scan lines in a frame, and the scan line numbering starts at 1).

PAL: 50 fields per second, 625 lines, odd lines drawn first

NTSC: 59.94 fields per second, 525 lines, even lines drawn first