[continued from previous message]
1 7
A. Reserved 1. /EXTSEL External Select (Input)
B. /IRQ Interrupt Request (Input) 2. /RST Reset (Output)
C. /HALT (Input) 3. D1XX /CS Chip Select $D1xx (In)
D. A13 Address Line 13 (Output) 4. /MPD Math Pack Disable (Input)
E. A14 Address Line 14 (Output) 5. AUDIO Audio In (Input)
F. A15 Address Line 15 (Output) 6. /REF Refresh (Output)
H. GND Ground 7. +5V
Keyboard port (XE System console only):
8 1
o o o o o o o o DA-15 Plug - male
o o o o o o o - pin numbering reverse of standard
15 9
1. /K2 Keyboard Scan (POKEY) 9. +5V
2. /K1 Keyboard Scan (POKEY) 10. +5V
3. /K0 Keyboard Scan (POKEY) 11. KBDETECT (GTIA/FGTIA)
4. /KR1 Keyboard Response (POKEY) 12. NC Not Connected
5. /K5 Keyboard Scan (POKEY) 13. GND Ground
6. /K4 Keyboard Scan (POKEY) 14. NC Not Connected
7. /K3 Keyboard Scan (POKEY) 15. GND Ground
8. /KR2 Keyboard Response (POKEY)
------------------------------
Subject: 1.16) Who designed the Atari 8-bit computers?
Many people were involved in the planning, design and engineering of the 8-bit Atari computers. This section attempts to identify the key engineering personnel at Atari and their roles, with the understanding that such a list necessarily oversimplifies the true nature of complex product development.
Some sources:
https://archive.org/details/JoeDecuirEngineeringNotebook1977, https://archive.org/details/JoeDecuirEngineeringNotebook1978, http://dougneubauer.com/atari/,
Goldberg/Vendel, Atari Inc.: Business is Fun, 2012, pp. 446-461, 694-700.
Atari 400/800 hardware designers:
Steven T. Mayer - Chief system inventor/architect, SVP engineering
Jay G. Miner - Project manager, system architecture
Douglas G. Neubauer - POKEY designer (also wrote Star Raiders)
Joseph C. Decuir - System co-inventor/co-architect; ANTIC designer
George McLeod - CTIA/GTIA logic designer
R. Scott Scheiman - Digital circuit designer; serial bus protocol
Francois Michel - ANTIC logic co-designer
M. John Ellis - VP engineering
Stephen D. Bristow - VP engineering
Wade B. Tuma - Director of engineering
Niles E. Strohl - Project engineering
John Vurich - Product marketing manager
Kevin P. McKinsey - 800 industrial designer (case)
Hugh M. Lee - 800 industrial designer (case)
Jeffery O. Nelson - 400 industrial designer (case)
Douglas A. Hardy - 400 industrial designer (case)
- Other notable contributors:
- VP research and development Al Alcorn
- Director of research Bob Brown
- Programmers Al Miller, Larry Kaplan, Bob Whitehead
- Cyan Engineering unit engineers including Ron Milner
- Chipset development technicians: Jim Luby (ANTIC), Steve Smith (CTIA),
Mark Shieu (POKEY), Steve Stone (POKEY), Delwin Pearson (POKEY)
Atari 1200XL/600XL/800XL hardware research & development (Atari NY Lab):
Steven T. Mayer - VP research and product development, Corporate Research Gregg Squires - Project Manager, Engineering Designer
Robert (Bob) Card - Principal Engineer
Steven Ray - Critical Electronics Layout Designer
Joel Moskowitz - Mechanical Engineer
Philippe des Rioux - Project engineer
Glenn Boles - Project engineer
Atari 1200XL/600XL/800XL hardware designers (California):
Ajay Chopra - System architect, 1200XL product specification author,
600XL/800XL Parallel Bus Interface specification
David Owen Sovey - Product engineering; 1200XL product specification
Larry Plummer - Director of engineering; 1200XL product specification Gene B. Rosen - VP engineering - 1200XL
David R. Stubben - VP engineering - 1200XL/600XL/800XL
Mark Lutvak - Product marketing manager - 1200XL
Andrew Soderberg - Product marketing manager - 600XL/800XL
Regan L. Cheng - Industrial designer (cases)
Atari 800XL("800XLF","SECAM ROSE")/65XE/130XE hardware designers:
Phil Suen - Director of engineering - XL/XE computers
Thomas B. Brightman - VP engineering
Richard C. Pasco - FREDDIE logic design
Bryan Kerr - Product marketing manager
Ira Velinsky - 65XE/130XE industrial designer (case)
XEgs/800XE hardware designers:
Jose A. Valdes - Development engineer
Ira Velinsky - Industrial designer (cases)
Atari Operating System designers and programmers are given elsewhere in this FAQ List.
------------------------------
Subject: 1.17) How do I use my Atari computer system?
This FAQ List is intended to answer many questions commonly asked about the 8- bit Atari computers, but one thing it doesn't do is offer a tutorial on basic usage of the system. Many such books were published, including those listed here. "Your Atari Computer" by Poole is often recognized as a classic among these.
[400/800]
Your Atari Computer: A Guide to Atari 400/800 Personal Computers
Lon Poole with Martin McNiff & Steven Cook, 1982 www.atarimania.com/documents/Your-Atari-Computer.pdf
User's Handbook to the Atari 400/800 Computers
Jeffrey R. Weber and Stephen J. Szczecinski, 1983 www.atarimania.com/documents/Users-Handbook-to-the-Atari.pdf
Get More From the Atari, Ian Sinclair, 1983 www.atarimania.com/documents/Get_More_From_The_Atari.pdf
[400/800/1200XL]
The User's Guide to Atari 400-800-1200XL Computers, Software, & Peripherals
By the editors of Consumer Guide, 1983 www.atarimania.com/documents/The-Users-Guide-to-the-Atari.pdf
How to use Atari Computers: An Introduction to the 400, 800, and 1200
Michael Boom, 1983
www.atarimania.com/documents/How-to-Use-Atari-Computers.pdf
Atari for the Beginning Beginner, Judy Chamberlain and Tom Chamberlain, 1983 www.atarimania.com/documents/Atari-for-the-Beginning-Beginner.pdf
[600XL/800XL, and also earlier models]
Your Atari Computer: A Guide to Atari 400/800 Personal Computers - XL Edition Lon Poole with Martin McNiff & Steven Cook (1983?) www.atarimania.com/documents/Your-Atari-Computer-XL-Edition.pdf
The Elementary Atari, William B. Sanders, 1983 www.atarimania.com/documents/The-Elementary-Atari.pdf
Atari XL User's Handbook, by WSI Staff, 1984 www.atarimania.com/documents/Atari_XL_User_s_Handbook.pdf
Getting Started with the Atari 600XL, Peter Goode, 1984 www.atarimania.com/documents/Getting_Started_with_The_Atari_600XL.pdf
The Atari 800XL: A Practical Guide, Thomas Blackadar, 1984 www.atarimania.com/documents/The-Atari-800XL-A-Practical-Guide.pdf
The Atari XL Handbook, Peter Lupton & Fraser Robinson, 1984 www.atarimania.com/documents/The_Atari_XL_Handbook.pdf
The Atari User's Encyclopedia, Gary Phillips and Jerry White, 1984 www.atarimania.com/documents/The-Atari-Users-Encyclopedia.pdf
InfoWorld's Essential Guide to Atari Computers, Scott Mace, 1984 www.atarimania.com/documents/InfoWorlds-Essential-Guide-to-Atari.pdf
How to Excel on Your Atari 600XL and 800XL, Timothy O. Knight, 1985 www.atarimania.com/documents/How_To_Excel_On_Your_Atari.pdf
[65XE/130XE, and also earlier models]
Atari XE User's Handbook, by Weber Systems, Inc. Staff, 1985 www.atarimania.com/documents/Atari_XE_User_s_Handbook.pdf
The Atari 130XE Handbook, Peter Lupton & Frazer Robinson, 1985 www.atarimania.com/documents/The_Atari_130XE_Handbook.pdf
------------------------------
Subject: 2.1) What are analog TV broadcasting systems and composite video?
The video display capabilities of the Atari computer are intimately related to the television (TV) broadcast systems of their time because, in part, consumer TVs were expected to be the primary display devices used with the system. The Atari was designed with the ability to output an analog radio-frequency (RF) audio/video signal that could be interfaced with a TV's antenna input, the input normally be used to receive terrestrial TV signals broadcast over the air.
The analog black-and-white RF television broadcast system standards that originally emerged throughout the world included System M (1941), System B (1950s), System I (1962), and System L (1967), plus System G. Broadcast signals compliant with these standards carried both audio and luminance ("Y") video information (plus synchronization information):
System M: o 525 scan lines per frame
o 486 scan lines of video per frame including overscan
o 262 scan lines per field (frame = two interlaced fields)
o 243 scan lines of video per field including overscan
o 60 fields per second = 60Hz
(refresh rate corresponds to household electricity standard)
o Complete frame refresh rate = 30 frames per second (fps)
o 4:3 aspect ratio
o System M was used in most of the Americas and Caribbean,
South Korea, Taiwan, Philippines, Brazil, and Laos.
o Japan used System J which was nearly identical to System M.
o Used with both very high frequencies (VHF channels 2-13) and
ultra high frequencies (UHF channels 14-83)
Systems BGIL: o 625 scan lines per frame
o 576 scan lines of video per frame including overscan
o 312 scan lines per field (frame = two interlaced fields)
o 288 scan lines of video per field including overscan
o 50 fields per second = 50Hz
(refresh rate corresponds to household electricity standard)
o Complete frame refresh rate = 25 fps
o 4:3 aspect ratio
o While G and I used the same UHF channel frequencies for
video carriers, they each used different audio carrier
frequencies for the same channels.
o B was used with VHF channels, while G was used with UHF
channels. B/G were used together in most of western Europe.
o System I was used in the UK over UHF channels only.
(The UK used System A over VHF channels until 1985.)
o System L was used in France over UHF only until 1984, with
VHF switching from System E to System L in 1984.
o Argentina used System N, which used frame parameters
matching those of B/G/I/L, but bandwidth parameters nearly
identical to System M.
Later, color (chrominance, or "C", being a combination of hue ("U") and saturation ("V") information) video encoding standards were adopted for combined use with the existing underlying RF broadcast system standards.
Three analog video color encoding standards that emerged in different parts of the world were NTSC ("National Television Standards Committee"; 1953), PAL ("Phase Alternation by Line"; 1967), and SECAM ("Sequentiel couleur avec memoire"; 1967). NTSC was used in most countries using the System M broadcast standard, while PAL was used in countries using Systems B/G and System I, and SECAM was used in France over System L. Thus NTSC M, PAL B/G, and PAL I, plus SECAM L in France, became the most common color TV broadcast systems used around the world. Outliers: PAL N in Argentina/Paraguay/Uruguay; PAL M in Brazil; NTSC J in Japan.
NTSC M actually and officially uses a slightly altered System M, where the frame rate is approximately 59.940 fields per second, or 29.970 frames per second (fps). PAL B/G, PAL I and SECAM L frame rates are exactly 25 fps.
In the 1970s a commercial market emerged for video display devices that would be compatible with existing TV broadcast standard video, but where the RF modulation/demodulation circuitry for transmitting/receiving audio/video broadcast signals over the air was omitted. Such a video signal, containing both luminance (Y) and (optionally) chrominance (C) information, but no audio, became known as composite video (often just "video"). A color composite video signal can be characterized by the color encoding standard used, one of the same standards invented for broadcast television: NTSC, PAL, or SECAM.
The luminance (Y) and chrominance (C) components that make up a color
composite video signal can also be transmitted as two separate signals. Such video is known as Y/C video, or S-video. Like both analog broadcast TV
signals and color composite video, Y/C video can also be characterized by the color encoding standard used: NTSC, PAL, or SECAM.
A monochrome composite video signal contains luminance (Y) information but no chrominance (C) information, and is typically characterized by its refresh rate: 60Hz (System M compatible) or 50Hz (Systems B/G/I/L/N compatible).
Each Atari computer version was designed to comply with video system standards used in the destination target market for that unit. Atari produced versions of their computers for NTSC, PAL, and SECAM markets, supporting combinations
of color analog RF broadcast standards (NTSC M, PAL B, PAL G, PAL I), color composite video standards (NTSC, PAL, SECAM), composite luminance signals ("Y"), and composite chrominance signals ("C"; NTSC or PAL) as follows:
RF Out Ch. ../ Monitor Port \...
to TV Composite "Y" "C" Computer Model Versions
NTSC M 2/3 - - - 400,600XL
NTSC M 2/3 NTSC 60Hz NTSC 800,65XE,130XE
NTSC M 2/3 NTSC 60Hz - 1200XL,800XL
NTSC M 2/3 NTSC - - XEgs
PAL B 3/4 - - - 400
PAL B 4 PAL 50Hz PAL 800,800XL(later),130XE,800XE
PAL B 4 PAL 50Hz - 800XL(earlier)
PAL B 4 PAL - - 600XL,XEgs
PAL G 36 - - - 400
PAL G 36 PAL 50Hz PAL 800,800XL(later),65XE,130XE,800XE
PAL G 36 PAL 50Hz - 800XL(earlier)
PAL G 36 PAL - - 600XL,XEgs
PAL I 36 - - - 400
PAL I 36 PAL 50Hz PAL 800,800XL(later),65XE,130XE
PAL I 36 PAL 50Hz - 800XL(earlier)
PAL I 36 PAL - - 600XL,XEgs
* * SECAM - - 800XL,130XE,XEgs
* monitor port includes provisions for an external in-line RF modulator
------------------------------
Subject: 2.2) What kinds of TVs can display my Atari's RF output signal?
An Atari 8-bit computer produces a single video display channel and a single (monophonic) audio channel. The 400/800 models also produce some sounds (primarily the keyclick and system buzzer sounds) by way of an internal speaker.
Most Atari computers provide both their audio and video channels in a single Radio-Frequency (RF) modulated audio/video signal, equivalent to a standard
(of the time) analog television (TV) NTSC or PAL encoded color broadcast signal. The Atari's RF signal may be used on a television that:
- Supports use of an external RF aerial antenna for receiving terrestrial TV
broadcast signals
- Can decode an analog NTSC M, PAL I, PAL G, or PAL B color TV broadcast
RF signal, matching the RF signal output by the computer
NTSC M Atari computers (North America) use:
- TV Channel 2 standard: 55.25MHz video carrier, 59.75MHz audio carrier
- TV Channel 3 standard: 61.25MHz video carrier, 65.75MHz audio carrier
PAL I Atari computers (UK) use:
- TV Channel 36 standard: 591.25MHz video carrier, 597.25MHz audio carrier
PAL G Atari computers (Europe) use:
- TV Channel 36 standard: 591.25MHz video carrier, 596.75MHz audio carrier
NOTE: If a PAL I computer connected to a PAL G TV, or PAL G computer is
connected to a PAL I TV, the result is normal video but lacking audio.
PAL B Atari computers (Europe, including: Germany, Italy, Finland) use:
- TV Channel 3 standard: 55.25MHz video carrier, 60.75MHz audio carrier
(400, some 600XL)
- TV Channel 4 standard: 62.25MHz video carrier, 67.75MHz audio carrier
- Equivalent to Channel B in Italy
(SECAM Atari computers (France) do not output an RF signal.)
The Atari's RF signal is accessed in one of the following places on the computer:
400/800: Built-in coaxial cable with male phono plug (NTSC computer
versions) or male Belling-Lee TV aerial plug (PAL computers)
XL/XE: Switch Box / Television jack (phono jack - female)
Domestic 400/800/XL/XE computers (NTSC M) shipped with a TV Switch Box (CA010112 / CA014746 packaged). This includes a phono jack (female) for RF signal input from the Atari, input connector(s) for your TV/cable/satellite antenna, and 75-ohm and/or 300-ohm output connector(s) for connection to the antenna input on the television. (For optimal signal quality, a simple
adapter (phono socket - female to F connector plug - male) in place of the standard TV Switch Box may be preferred.)
Domestic XL/XE computers (NTSC M) shipped with a coaxial RF Cable / TV Video Cable (1200XL: CA061177 - 12 feet; other XL/XE: CA024624 toroid cable Domestic/NTSC versions). The input end is a phono plug (male) that plugs into the Switch Box/Television jack on the computer; the output end is also a phono plug (male).
PAL/UK XL/XE computers (PAL B/G or PAL I) shipped with a coaxial RF Cable / TV Video Cable (CA024624 Toroid Cable PAL versions). The input end is a phono plug that plugs into the Switch Box/Television jack on the computer; the
output end is a TV aerial plug (Belling-Lee plug - male).
------------------------------
Subject: 2.3) What kinds of computer monitors can I use with my Atari?
An Atari 8-bit computer produces a single video display channel and a single (monophonic) audio channel. The 400/800 models also produce some sounds (primarily the keyclick and system buzzer sounds) by way of an internal speaker.
While most Atari computers provide an RF color television signal (described in another section of this FAQ list), many also (or alternatively) provide a composite video signal, and some also provide a composite luminance signal ("Y") or a composite chrominance signal ("C") or both, which together are
known as Y/C video or S-video. The French Peritel 400/800 provide limited palette RGB video signals.
Except for the NTSC and PAL versions of the XE System console, Atari computer versions that provide composite, "Y", or "C" video signals output them through the computer's Monitor port, which also contains a line for the computer's audio output. The pinouts for the Atari Monitor ports are in the pinouts section of this FAQ list.
The XE System console (all versions) provides a phono Video jack for composite video output, and a phono Audio jack for the computer's audio output.
Color Composite Video Monitors
==============================
An 8-bit Atari computer, except the 400 and the NTSC version of the 600XL, provides an NTSC, PAL, or SECAM (depending on the computer version) composite video output signal. Any computer monitor, television, or video receiver that accepts a standard NTSC, PAL, or SECAM (matching the computer version) composite video input can be used with the Atari. For sound support, a
monitor that also accepts a separate sound input and has a built-in speaker could be used. Such monitors were common for use with home computers at the time of the Atari, in part because the picture quality was superior to that offered by TVs of the time. Modern devices that accept a composite video
input remain suitable as well.
The typical Atari (color) monitor cable includes the male 5-pin DIN connector on one end for the Atari Monitor port, and two phono plugs on the other end. One of the phono plugs will carry the monophonic sound signal, and the other will carry the composite video signal. Atari's own CX89 Color Monitor Cable
is of this type.
Monochrome Composite Video Monitors
===================================
Many 8-bit Atari computer models, including the 800, 1200XL, 800XL, 65XE, 130XE, and 800XE, provide a composite luminance video output signal ("Y").
The video signal refresh rate corresponds to the computer version: 60Hz on
NTSC computer versions or 50Hz on PAL computer versions. Any computer
monitor, television, or video receiver that accepts a standard 60Hz or 50Hz (matching the computer version) monochrome composite video input can be used with the Atari. For sound support, a monitor that also accepts a separate sound input and has a built-in speaker could be used. At the time of the
Atari a monochrome composite monitor, when compared to a color composite monitor, was less expensive and generally provided a sharper and easier to
read image. The monitor reduces the Atari's color graphics output to shades
of green or amber (depending on the monitor), making the display less suitable for entertainment or education software, but more suitable for productivity applications.
An Atari monochrome monitor cable includes the male 5-pin DIN connector on one end for the Atari Monitor port, and two phono plugs on the other end. One of the phono plugs will carry the monophonic sound signal, and the other will carry the composite luminance "Y" signal. Atari's own CX82 Black and White Monitor Cable is of this type.
The Atari XEP80 Interface Module can be used to add a high-resolution monochrome composite video output to any 8-bit Atari computer. The XEP80 is detailed elsewhere in this FAQ list.
Y/C Video (S-Video) Monitors
============================
Some 8-bit Atari computer models, including the 800, 800XL (later PAL units), 65XE, 130XE, and 800XE, provide both a composite luminance video output signal ("Y") as well as an NTSC or PAL (depending on the computer version) composite chrominance output signal ("C"). Any computer monitor, television, or video receiver that accepts standard NTSC or PAL (matching the computer version) Y/C video, also known as S-video, can be used with the Atari. For sound support, a monitor that also accepts a separate sound input and has a built-in speaker could be used. Y/C video quality is superior to color composite video,
making supporting display devices the ideal for use with the Atari. Such monitors were highly sought after by savvy Atari users of the time.
The most flexible type of Atari monitor cable includes the male 5-pin DIN connector on one end for the Atari Monitor port, and includes 4 phono plugs at the output end, carrying the monophonic sound signal, the composite video signal, the composite luminance ("Y") signal, and the composite chrominance ("C") signal. Such a cable can be used to connect an Atari to a color monitor accepting separate "Y" and "C" inputs, to a color composite monitor, or to a monochrome composite monitor. (Atari themselves did not produce a monitor cable of this type.)
While the best color composite monitors of the time of the Atari accepted "Y" and "C" signal inputs through phono jacks, more modern television or video receivers may accept these input signals together in the form of an S-video Mini4 connector. "Atari to S-video" interfaces or cables allow such modern devices to work nicely with the highest quality video output signal produced
by the Atari.
Television Sets in France
=========================
Entering the French market with the 400/800 was a challenge for Atari because they lacked SECAM versions of the computers to sell, and newer TVs also supporting PAL video were not yet widely available. Atari's initial
workaround to support more French TVs was to offer PAL G computer versions modified to additionally provide an RGB video signal. It was only a partial solution, because the Atari's RGB signal output had a limited palette of only
8 possible colors, derived from the 8 luminance/brightness levels as generated by GTIA. Native Atari PAL color/hue information was ignored.
The 400 Peritel version has a built-in TV connecting cable that terminates
with a Peritel connector. The 800 Peritel version was supplied with a cable that plugs into the 800 Peritel Monitor port (8-pin DIN) at one end, with the Peritel connector at the other end. 400/800 Peritel cable connector pinout:
6. Audio (mono)
7. RGB Blue _20_________________2_
8. Slow Switching (+12V = AV Mode 4:3) \ o o o o o o o o o o |
11. RGB Green (21)\ o o o o o o o o o o|
15. RGB Red 19------------------1
16. Fast Switching (High / +1-3V = RGB)
17. Video Ground Not connected: pins 1-5,9-10,12-14,18-19
20. RGB Sync
see:
http://atariage.com/forums/topic/252426-400pal-with-rf-and-scartperitel/
http://www.atari800xl.eu/hardware/computers/peritel-atari-800.html
http://www.atari800xl.eu/hardware/computers/peritel-atari-400.html
When development of native SECAM versions of the 600XL/800XL was delayed Atari chose to supply (unmodified) PAL G 600XL/800XL computers in France, as TVs supporting PAL video were becoming more common. Yet, to support older televisions requiring SECAM or RGB video, Atari also separately offered the Adaptateur PAL/Peritel PVP80 (by Compagnie Generale de Videotechnique or CGV) to provide an RGB video signal (and audio) via Peritel connector. The PVP80 plugs into the 600XL/800XL monitor port (5-pin DIN) at one end, with the Peritel connector at the other end. PVP80 Peritel connector pinout:
4. Audio Ground
6. Audio (mono)
7. RGB Blue _20_________________2_
8. Slow Switching (+12V = AV Mode 4:3) \ o o o o o o o o o o |
11. RGB Green (21)\ o o o o o o o o o o|
15. RGB Red 19------------------1
16. Fast Switching (High / +1-3V = RGB)
17. Video Ground Ground: 4,5,9,13,17,18
20. RGB Sync Not connected: pins 1-3,10,12,14,19
The standard video cable provided by Atari France with SECAM 800XL, 130XE and XE System console units has the male 6-pin DIN on the end that plugs into the computer's Monitor port, and a Peritel connector on the other end, with this pinout:
2. Audio (tied to pin 6) _20_________________2_
4. Audio Ground (tied to pin 17) \ o o o o o o o o o o |
6. Audio (tied to pin 2) (21)\ o o o o o o o o o o|
8. Slow Switching (+12V = AV Mode 4:3) 19------------------1
16. Fast Switching (Low / not connected = Composite)
17. Video Ground (tied to pin 4)
20. Composite video (SECAM standard)
Not connected: pins 1,3,5,7,9-16,18-19
------------------------------
Subject: 2.4) What were the Atari XC1411 and XM128 monitors?
Introduced in January 1985, the Atari XC1411 monitor was a 14" color composite video monitor with built-in speaker, styled to match the Atari XE computers. There were two phono jacks, one for composite video and one for sound, and units were in the same case as the original Goldstar-produced Atari SC1224 monitor for Atari ST computers. The XC1411 never shipped, and no more than a handful of prototype units may exist.
Introduced in January 1985, the Atari XM128 monitor was a 12" green monochrome composite monitor, styled to match the Atari XE computers, suitable for high- resolution 80-column text display. The XM128 never shipped, and no more than
a handful of prototype units may exist.
------------------------------
Subject: 2.5) What are composite video artifact colors, or artifacts?
Much of this section derived directly from De Re Atari, Appendix D:
"Television Artifacts":
http://www.atariarchives.org/dere/chaptD.php
Appendix D is credited to Atari's Lane Winner with assistance from Jim Cox.
Composite video artifact colors arise when a spot or "pixel" on the screen displays a different color than the one assigned to it.
The possibility of artifacting is inherent to the nature of an NTSC or PAL composite video signal. The two major components of this signal are the luminance, or brightness, and the color, or tint. The luminance information
is the primary signal, containing not only the brightness data but also the horizontal and vertical syncs and blanks. The color signal contains the color information and is combined or modulated into the luminance waveform.
The luminance of a pixel on the screen is directly dependent on the amplitude of the luminance signal at that point. The higher the amplitude of the signal, the brighter the pixel.
The color information, however, is a phase shifted signal. A phase-shifted signal is a constantly oscillating waveform that has been delayed by some amount of time relative to a reference signal, and this time delay is translated into the color.
In the NTSC standard, the color signal, or color subcarrier, oscillates at a constant rate of 315/88 MHz (approximately 3.579545 MHz or 3.58 MHz). In the PAL standard, the color subcarrier is 4.43361875 MHz. These color subcarrier frequencies set an upper boundary to the horizontal color resolution of an
NTSC or PAL composite video signal. The horizontal unit of maximum resolution for color composite video is known as the color cycle.
The Atari's system timing is built around the timing of the composite video color cycle. The Atari term "color clock" refers to one color cycle and is
the term generally used throughout the Atari documentation to describe units
of measurement across the screen. The OS graphics mode 7 (ANTIC mode D) is an example of one color clock resolution, where each color clock pixel can be a different color, for a horizontal resolution of 160 pixels in the playfield.
The Atari also offers "high resolution" graphics, where pixel width is half that of a color clock.
Since the luminance is the primary part of the composite video signal,
whenever it changes, it also forces a change in the color phase shift. For
one or more color clocks of constant luminance this is no problem, since the color phase shift will be unchanged in this area. However, if the luminance changes on a half color clock boundary it will force a fast color shift at
that point.
For the NTSC Atari, where a machine cycle is precisely 1/2 of the NTSC color subcarrier frequency, varying the amplitude of the luminance signal at twice the color clock frequency (2*3.58MHz) also means generating a signal at
exactly twice the NTSC color subcarrier frequency. The result is stable NTSC color information for that pixel that was not generated as color information
by the Atari.
Since the luminance can change on half color clock boundaries, this implies that two false color, or artifact pixel types can be generated. This is basically true. However, these two pixels can be combined to form two types
of full color clock pixels. This is illustrated below:
TV Scan | | |
Line |<---1 color clock---->| |
| | |
| | | | |
|<-1 pixel->| | | |
| | | | |
Luminance 0 1 0 0 1/2 cc pixel color A
(0=off, 1 0 0 0 1/2 cc pixel color B
1=on) 1 1 0 0 1 cc pixel color C
0 1 1 0 1 cc pixel color D
The actual colors A,B,C,D seen depends upon the version of the NTSC Atari computer used, due to variances in the designs of the video signal generation electronics leading to slightly different timings of fast color shifts and
thus different sets of artifacting colors.
With an NTSC Atari, the ANTIC screen modes capable of artifacting colors on
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