more rs-170

[P3D Bob Wier <wier@xxxxxxxxxxxxxxxxxxxxxxxx>]

RS-170
The EIA (Electronics Industries Association) standard that defines the
timing of broadcast video in the United States, Japan, and several
other markets. It specifies a 15.75-KHz horizontal and a 60-Hz
vertical interlaced scan frequency as well as other aspects of the
composite signal such as voltage, sync levels and timing of blanking.
Interlacing is the process by which two fields, called scan lines, are
interleaved on the screen. Due to the limitations of video devices at
the time the standard was being set in 1957, the speed of broadcast
signals and picture tubes required the image to be displayed in parts.

The solution allowed the partial update of video pictures to remain
unnoticed to the viewer. An RS-170 video frame contains 525 lines and
is displayed 60 times per second=93for a total of 15,750 lines, or 15.75
KHz. Of these lines, only the odd or even lines are displayed with
each frame. A total of 60 frames per second allows 30 frames per
second, or a 30-Hz update of each line.

Like the RS-343 standard, RS-170 is strictly a timing specification
for monochrome video signals. By combining three such signals to
control individual red, green, and blue sweep circuits, you can create
a full-color system. The RS-170 mode is available with the Macintosh
video card as a way for VCRs and large screen projectors, not capable
of high-frequency scans, to interface with the Macintosh.

Compare RS-343, RS-170A, RS-170 RGB.

RS-170 RGB
Refers to RGB signals timed to RS-170 specifications. Since the red,
green and blue signals are actually individual monochrome signals
representing their respective colors, RS-170 RGB merely refers to
three black and white signals sharing one sync signal which is either
provided separately as a fourth signal or (usually) combined with the
green signal. Compare RS-170A, RS-170.

RS-170A
Twenty years after the drafting of RS-170, the EIA video signal
standard proposal RS-170A evolved into what is known today as the NTSC
composite video signal. RS-170A specifies timing of scans (essentially
the same as RS-170: 15.732 KHz horizontal and 59.94 Hz vertical) and
blanking as well as the 3.58 MHz burst required to decode the color
signals. As adopted by the FCC for broadcast use, the standards are
precisely adhered to and carry the force of law. For non-broadcast
use, EIA standards are merely recommendations and are not enforced.
Specifications referring to RS-170A do not necessarily mean the
signals are broadcast standard. RS-170 RGB, RS-170.

RS-343
An EIA (Electronics Industries Association) standard for non-broadcast
high resolution monochrome video, specifying a 60 Hz non-interlaced
scan with a composite sync signal with timings that produce a
non-interlace (progressive) scan at 675 to 1023 lines.

While the Macintosh version of the RS-343 signal varies somewhat, it
essentially follows the guidelines necessary for connection to RS-343
display devices. Therefore, with a display adapter (available from
Covid , Extron, or Inline) the Mac can drive a RS-343 device (i.e.
video projector or large monitor).

The major differences between Macintosh video and the RS-343 standard
are: a separate TTL level composite sync signal on pin 3, the separate
video lines used to produce RGB color, a vertical scan rate of 66.67
Hz to reduce screen flicker, and a voltage white level of 1 volt for
its red and blue signals and 1.3 volts on its green signal. RS-343
provides for a 60-Hz signal but has been changed to 66.67 Hz on the
Macintosh video card to prevent the screen flicker which is visible at
60 Hz. The inclusion of the analog composite sync found on pin 5 of
the video card connector, called the green signal, allows for
monochrome composite video.

S-video
A consumer form of component video (Y/C) used primarily with Hi8 and
S-VHS equipment.



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