Video Signals
author Neil Franklin, last modification 2007.01.09


Original B&W TV

US 2*30 half-frames/s of 2*262.5 lines (15.75kHz/63.5us), 4/5 (2*210) shown
  line 4/5 of 63.5us (50.8us) shown, pixels at max 5.5MHz AC bandwidth
    chopping line into square pixels 4/3 * 2*210 = 560 (0.0907us/11MHz)
EU 2*25 half-frames/s of 2*312.5 lines (15.625kHz/64us), 4/5 (2*250) shown
  line 4/5 of 64us (51.2us) shown, pixels at max 6.5MHz AC bandwidth
    chopping line into square pixels 4/3 * 2*250 = 666.67 (.0767us/13MHz)
signal is combination of brightness information (4/5 of line)
  and backtrace (1/5 of line) including synchronisation pulse
  1V at 75ohm, 0.7V brightness (0=white, 0.7=black) and 0.3V sync (1.0=sync)
often less line length is actually drawn, to get rid of overscan losses
  often (8*1)MHZ 320pixel in 40us (78%), or (14.318/2)MHz 256pixel 35.7us (70%)


NTSC and PAL colour TV
is above B&W TV, with colour added backwards compatible
brightness/luminance is computed as Y = 0.3*R+0.59*G+0.11*B
  and additionaly 2 "color difference" signals U = G-R and V = G-B
for NTSC(US) and PAL(EU) the U and V are then QAM modulated onto colour carrier
  NTSC carrier 3.579545MHZ with 0.5MHz(down)/1.3MHz(up) bandwidth
    4 times this is 14.318180MHz quarz, div by 3 gives original PC 4.7727266MHz
    div by 4 gives many Z80 3.5785450MHz, div by 14 gives NTSC C64 1.0227271MHz
  PAL carrier 4.433619MHZ with 1.5?MHz(symmetrical) bandwidth
    4 times this is 17.734476 quarz, div by 18 gives PAL C64 0.9852486MHz
for SECAM the U and V are then alternatingly FM modulated onto colour carrier
  SECAM same freq to PAL, just different colour carrier and modulation


PC MDA (Mono Display Adaptor)
B&W character-only display 80x25 with 9x14 font, so 720x350 pixels
  80x25 (=2000, not quite 2k) chars of each 2byte (1 char, 1 attrib) = 4k RAM
50 full-frames/s of 368 lines (18.43kHz/54.3478us), 350 shown
  uses non-square pixels, clocked 16.257MHz, 883pixels/line, 720 shown
not compatible with TV technology so can deviate in signalling, uses pure TTL
  2bit digital brightness, and 2 separate 1bit H and V sync
  3 gray levels (BI: 00=black, 10=normal (light gray), 11=bright (white))
DB9 connector 1+2 GND, 3+4+5 nc, 6 Intensity, 7 Brightness, 8 HSync, 9 VSync
  HSync positive, VSync negative active


PC MGA (Mono Graphics Adaptor) a.k.a Hercules
uses same monitor as MDA, same signals, same text mode, that was selling point
  just additional 720x384 pixels 1bpp (=32k RAM) graphics mode


PC CGA (Color Graphics Adaptor)
(and many home computers and video consoles, Apple, Atari, Commodore, ...)
missuse of NTSC or PAL TV as computer monitor, freq see there
  60/50 full-frames/s by doing 262 or 312 lines (-0.something%)
40|80x25 chars of 8x8 pixels (=320|640x200 pixels)
  or 320|640x200 pixels 2 or 1bpp graphics
  40x25 (= 1000, not quite 1k) chars of each 2byte (1 char, 1 attrib) = 2k RAM
  80x25 (= 2000, not quite 2k) chars of each 2byte (1 char, 1 attrib) = 4k RAM
  320|640x200 (= 16000, not quite 16k) 8pixel@1bpp|4pixel@2pbb = 16k RAM
  uses non-square pixels, clocked 7.159|14.318MHz, 450|910pixels/line
    360|720pixels drawn (non sync), actually 320|640 data, 40|80 overscan
Cinch connector standard NTSC TV video signal
DB9 connector 1+2 GND, 3+4+5+6 Red+Green+Blue+Intensity, 7 nc, 8 HSync, 9 VSync
  HSync positive, VSync positive active


PC/AT EGA (Enhanced Graphics Adaptor)
merged near-MDA text quality and above-CGA colour facilities
  80x25 chars of 8x14 pixels (=640x350 pixels)
  or 640x350 pixels 1bpp or 4bpp graphics
60 full-frames/s of 363 lines (21.80kHz/45.8715us), 350 shown
  uses non-square pixels, clocked 16.257MHz, 746pixels/line, 640 drawn
not compatible with TV technology so can deviate in signalling, pure TTL
  uses 3*2bit digital brightness (= 64 colours), and 2 separate H and V sync
DB9 connector 1 GND, 2-7 Red0+Red1+Green1+Blue1+Green0+Blue0, 8 HSync, 9 VSync
  HSync positive, VSync negative active


PC/AT PGA (Professional Graphics Adaptor)
no details known to me, apart from 4096 (=3*4bit) colour palette (like Amiga)


PS/2 and PC VGA (Video Graphics Array/Adaptor)
above-MDA text quality and above-EGA colour facilities
  80x25 chars of 9x16 pixels (=720x400 pixels)
  or 640x480 pixels 4bpp graphics
  or 320x200 pixels 8bpp graphics
70 full-frames/s of 450 lines (31.50kHz/31.75us), 400 shown for text mode
  uses non-square pixels, clocked 28.32MHz, 900pixels/line, 720 drawn
60 full-frames/s of 525 lines (31.50kHz/31.75us), 480 shown for graphics mode
  uses square pixels for first time, clocked 25.18MHz, 800pixels/line, 640 dra
HD15 connector 1+2+3 Red+Green+Blue, 4 ID2, 5 nc, 6+7+8 GND-Rd+GND-Gr+GND-Bl
  9 mark (no hole), 10 GND-Sync, 11+12 ID0+ID1, 13 HSync, 14 VSync, 15 nc
  HSync negative, VSync negative active (text mode)
  HSync negative, VSync positive active (graphics mode)


PS/2M30 MCGA (???)
VGA reduced to 64k video RAM, 640x480 pixels only 1bpp, full 320x200 8bpp


PS/2 and PC 8514/A
1024x785 4bpp with 2*43.5 half-frames/s, no further details known to me


later PC display types are ignored, are just VGA with more speed and colours
  and vary from card to card, as now multisync monitors take over
  and become completely random with Linux XFree/x.org ModeLine settings