I have been searching for a Video Encoder (DAC) that can output composite signals that are EIA-170/RS-170 and SMPTE 170M standard compliant. I might not be understanding these standards correctly but it seems that I am finding encoder with either or but not both. My questions are:

  1. am I looking for something that doesn't exist?
  2. If the data sheet of the encoder says that it outputs NTSC composite video, doesn't that mean that it would cover both EIA-170/RS-170 and SMPTE 170M?
  • \$\begingroup\$ In short: "1: yes, 2: yes". More details in my answer below. \$\endgroup\$ Commented Sep 1, 2023 at 0:49

1 Answer 1


I haven't dealt in analog video in a while, but looking at the first datasheet I found NXP MC44722A, there is control in register 70 to turn off the color burst (it's ON by default).

My understanding is that a SMPTE170M encoding without the color burst and the setup pedestal set at 0IRE (register 72) would meet the recommendations of the RS-170 specification.

I've never used this chip in a design, but from reading the datasheet I gather it was designed as a universal composite encoder, which can encode a large variety of analog standards, including RS-170. Other encoders, would, with little doubt, be equally capable.

From a business perspective, I can't see a company like Philips designing a chip like this which is not also capable of meeting the RS-170 spec, so on the balance of probabilities, there would not exist a separate encoder that is specific to RS-170 encoding, offered along-side this, more capable, chip. Also, given the evolution of the digital video standards, it does not make sense for an encoder specific to RS-170 to exist (at the time the digital standards were invented, the monochrome RS-170 specification had already been long deprecated; only a digital to both color and monochrome analog encoder would make any sense).

I suspect the reason why encoder datasheets like the quoted one don't mention compatibility with RS-170 is that it was not an enforced standard, but a mere recommendation.

Update: I have just noticed some of your other related questions, and the chip SAA7104H, which does make reference to RS-170A, and is a PC graphics to composite video encoder (ie, has nothing to do with SMPTE 170M, which is a video standard), and based on these findings I suspect the problem you are facing is that you don't yet understand the problem space well enough to ask meaningful questions.

With this realization in mind, I would like to caution you to study the problem you're asked to solve in more depth. I suggest "Digital Television Fundamentals" by Robin and Poulin, which is a fairly comprehensive introduction to the technology you're venturing it. One concern you should have is video format (progressive vs analog). It makes some sense for a product that has a genlock input to also have a frame buffer, and take input from either a PC, but not much sense for it to take SMPTE 125M video input. In other questions, you use the term TMDS which suggests a graphics input rather than a video. I doubt what you're looking for is a DAC, and I suspect you're looking for a graphics to video encoder instead.

You should describe your application, rather than cite acronyms that are not in your vocabulary.

Anyway, my answer above assumes you're looking for a digital to analog composite video encoder, and thus responds to your query as asked, although now I understand the answer you need is the "Digital Television Fundamentals" recommendation, instead.

  • \$\begingroup\$ I'm pretty sure SMPTE 170M is not a digital video standard. I also did mention that I am using a video encoder, but you mention that I should look for a graphics to video encoder. I thought TMDS and HDMI, though different are very similar? Didn't know they existed (graphics to video encoder) but I'll look into those. Thank you for the recommendation though. \$\endgroup\$
    – miggyEE
    Commented Sep 1, 2023 at 22:25
  • \$\begingroup\$ The title of SMPTE 170M is "Television - Composite Analog Video Signal - NTSC for Studio Applications", and SMPTE stands for "Society of Motion Picture and Television Engineers", so yes, SMPTE 170M is decidedly a video standard. I should not have said a "digital video standard" but a "video standard", as opposed to "computer graphics". I will edit this mistake. The key is that is deals with interlaced video at 59.94Hz refresh rate, while it seems to me you're handling progressive content at some unspecified, possibly not fixed, frame rate. \$\endgroup\$ Commented Sep 1, 2023 at 22:37
  • \$\begingroup\$ TMDS is an encoding of data onto serial mediums, with the principal role of making cables cheaper. While it is used in HDMI and other interfaces, TMDS and HDMI are not synonyms, nor comparable terms. One refers to how data is encoded, the other refers to the physical interface and data formatting. \$\endgroup\$ Commented Sep 1, 2023 at 22:46
  • \$\begingroup\$ thank you for the clarification. The frame rates for the RS-170 and SMPTE 170M are 30Hz and 29.97Hz respectively. \$\endgroup\$
    – miggyEE
    Commented Sep 1, 2023 at 22:50
  • \$\begingroup\$ This is what I mean when I say you conflate video and graphics. The word "frame rate" is graphics terminology, and is correctly quoted in frames per second, not Hz, while video uses "field rate", "refresh rate", and is correctly quoted in Hz, not frames per second. Hz is a measurement of something periodic, like a frequency, while frames per second is not necessarily periodic. It seems like you should be able to divide the numbers readily, and ignore the units, or mix and match at will, which is fine for casual conversation, but incorrect technical terminology. \$\endgroup\$ Commented Sep 2, 2023 at 0:45

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