- We have a new product out for sale! Wii YPbPr component cables can now be purchased via our Amazon store. You may notice that they also come in a shiny new box with a bunch of boring warnings and symbols plastered all over it. We'll eventually port all our products over to new snazzy packaging, but in the near future it will just be the PS2 and Wii cables. Current Wii inventory may be a bit patchy as we only air shipped in a tiny batch, while the rest are due to arrive via ocean freight sometime in July.

- The next batch of Genesis YPbPr cables has landed! We'll start pushing these out to our distributors (Castlemania Games, RetroStuff Canada) in the coming week or so. Just like with SNES YPbPr cables, these will not be available on our Amazon store, so make sure you are set up to get the latest information from your preferred distributor(s).

- PlayStation 2, M-M RCA, and M-F extension YPbPr cables just wrapped up at the factory and are due to head our way via ocean freight soon. We're anticipating a mid-summer date for the full restock of those, but we air shipped ourselves a small batch of PS2 cables to get Amazon going in the meantime. Those should be found at the same Amazon link in about a week or so, assuming no issues are found during our standard QA check.

- Dreamcast development is chugging along and the end of the design phase is finally in sight. Last month, we resolved the last of the 21 known issues/bugs with the prototype circuit, and the overall results are looking fantastic on the workbench. We are now waiting for the factory to finishing sorting out a bunch of their overmolding requirements before we throw down a final circuit board layout. They're being slow about giving complete and thorough information about this, so in the meantime we are working on the design verification procedures and also the test equipment which needs to be in place for mass production.

Be sure to check us out on Twitter if you want more frequent updates!

That's all for now, folks!

Posted
AuthorNickolaus Mueller

One of the most common questions we get asked during The Retro Roundtable podcast is “What is the proper way to generate CSYNC from HSYNC and VSYNC?”. People understandably ask this because we’ve mentioned several times that nearly all implementations of this process are incorrect. The question is typically asked with the expectation that it can be quickly answered. I mean, if we’re able to so easily point out improper implementations, then shouldn’t we be able to just as easily explain the correct implementation? Unfortunately, this isn’t true with nuanced topics such as this one. Therefore, I’m going to try my best and explain this subject here in detail so it can be properly documented and easily referenced. I’ve determined that this information would be best presented and understood when split into 3 separate parts. Let’s begin with the first part which covers what CSYNC is and why it exists in the first place. This background is necessary for understanding the difficulties that arise with the proper creation of CSYNC from discrete HSYNC & VSYNC.

Defining “Sync”

Sync is short for synchronization, and refers to how a video system needs to be “locked on” or, in simpler terms, stabilized. CSYNC, or composite sync, can be described as a combined version of the HSYNC and VSYNC signals. Since CSYNC is defined by those two sub-components, we need to first understand them. HSYNC is horizontal sync and VSYNC is vertical sync. A video system’s end goal is to display an image on a 2D screen, where the two dimensions are horizontal and vertical. Therefore, HSYNC keeps the horizontal axis (each line) stable by defining the horizontal reference point, while VSYNC does the same thing for the vertical axis (each frame or field). Both of these references are required for the image to be properly reconstituted on a display device. An example showing the HSYNC and VSYNC waveforms for 60Hz standard definition video is shown below. As discussed in our Sync Jitter article, the falling edges of these waveforms represent the desired reference points (line start for HSYNC; field start for VSYNC). Note that in this example there are two unique fields which keep alternating between each other. The second field of each two-field sequence begins in between two lines and is used to achieve interlacing* as detailed further below in this article.

*NOTE: I’m not going to get into the whole concept of interlacing and why it was chosen for television broadcasting. The only thing required to know is how interlacing affects the structure of HSYNC & VSYNC and the encoding of CSYNC.

HSYNC and VSYNC waveforms representing 60Hz standard definition video. Line numbers are labeled as are the two unique fields required for interlacing.

HSYNC and VSYNC waveforms representing 60Hz standard definition video. Line numbers are labeled as are the two unique fields required for interlacing.

When monochrome (black&white) television broadcasting (as defined by RS-170/EIA-170) was first introduced in North America, a scheme needed to be devised to combine (encode) all the required audio & video information into a single signal for transmission over the airwaves. One of the steps involved in achieving this was to convey the HSYNC and VSYNC information in a way such that it can be interpreted and utilized by the display device to make the final image. “Information” is very crucial to emphasize here. Video cameras and other video source equipment destined for TV* consumption do not explicitly generate separate HSYNC and VSYNC signals which are later combined into CSYNC via a separate circuit or procedure. The CSYNC signal is generated directly in a manner where the underlying HSYNC and VSYNC data can be inferred by the circuitry in the target device. The takeaway here is that the explicit HSYNC and VSYNC signals are only ever accessed at the display side.

*NOTE: This discussion focuses only within the context of television. The modern computing and PC space handles things differently, where HSYNC and VSYNC signals are explicitly generated and transmitted over a short distance to the display (e.g. VGA cables).

Generating a Practical CSYNC

The most straightforward way of doing this would be to simply widen the HSYNC pulse whenever VSYNC is active [section (A) in the figure below]. The main problem with this is that a display device loses HSYNC lock during this portion. The solution is to introduce a series of wide pulses which still have falling edges where HSYNC falling edges would occur [section (B) in the figure below]. In analog video terminology, these are called “serrated pulses”. This should be all that’s needed, but in order to effectively implement the interlacing scheme used by standard definition TV, we require one more tweak. Because the VSYNC is offset by half a line (i.e. halfway between HSYNCs), double-pulses at twice the HSYNC rate are introduced in the areas around and including VSYNC [section (C) in the figure below]. During the 3 line period prior to VSYNC, there exist 6 “pre-equalization” pulses. Similarly, during the 3 line period after VSYNC, there are 6 “post-equalization” pulses. Additionally, the width of these equalization pulses is half the width of the normal HSYNC pulses. The evolution of this concept along with the various waveforms are shown below.

Evolution in the design of a proper CSYNC signal for practical transmission and recovery:  (A) = Naive direct logical combination of HSYNC and VSYNC  (B) = Addition of serrated pulses during VSYNC to keep HSYNC lock  (C) = Addition of double-pulses and shortened width for pre/post-equalization pulses to maintain interlacing

Evolution in the design of a proper CSYNC signal for practical transmission and recovery:

(A) = Naive direct logical combination of HSYNC and VSYNC

(B) = Addition of serrated pulses during VSYNC to keep HSYNC lock

(C) = Addition of double-pulses and shortened width for pre/post-equalization pulses to maintain interlacing

To validate the practicality of the finalized CSYNC waveform above, we can briefly examine simple examples* of how HSYNC & VSYNC can be recovered at the display side of the video system. Since this properly constructed CSYNC retains all of the original HSYNC’s falling edges, we can use those edges to trigger a monostable multivibrator (aka “one-shot”) to generate HSYNC pulses at their standard widths and at the correct locations. If required for a particular application, a second non-retriggerable one-shot, controlled by the same CSYNC input but with its output set just shy of the total line length (at about 95%), can be used to inhibit the output of the first one-shot in order to ignore the double-pulses during pre/post-equalization and VSYNC. For discrete VSYNC recovery from CSYNC, a simple two-stage RC integrator (filter) followed by an analog comparator set at a suitable threshold can be used to recover the wider VSYNC while ignoring all the shorter HSYNC pulses. An example circuit of this outlined VSYNC recovery method and its relevant waveforms are shown below.

*NOTE: These examples are highlighted and discussed for educational purposes only.

Simple RC integrator + analog comparator VSYNC recovery circuit.

Simple RC integrator + analog comparator VSYNC recovery circuit.

31 Flavors of 240p

The above CSYNC timing structures describe the 525-line 60Hz system (59.94Hz for color), or “480i” as it’s more commonly known today. 240p, in its most simple representation, is a slight variation on the above timing. Instead of drawing 262.5 lines in between each VSYNC edge to achieve interlacing, the idea is to have an integer number of lines which is needed for progressive scanning (the ‘p’ in 240p). There are two main ways of accomplishing this. Game consoles, retro computers, and various other devices are known to implement either one of these two types. You can either get rid of a half-line resulting in 262 lines, or add an additional half-line bumping you up to 263 lines. Regardless of which method is implemented, each field’s timing pattern now looks exactly the same, and the concept of first/second fields no longer applies. Therefore, the term “field” is dropped and the set of lines between each VSYNC edge is known as a frame. Because of all this, even more variations of 240p manifest themselves. The double-pulses no longer serve a practical purpose, so a common variation used by video equipment manufacturers is to remove them from the pre-equalization section, VSYNC serrated pulse section, and post-equalization section. On top of that, some implementations choose to also increase the widths of the shorter pulses during pre/post-equalization back to the normal HSYNC pulse width.

As you can see, it starts to get quite messy once 240p comes into play. A handful of some different possible 240p flavors are shown below. Although there are many combinations of these slight variations, not one of them is documented within a video standard. However, within most implementations of 240p CSYNC the critical properties of the timing structure stay intact, increasing the likelihood that the signal can be properly recovered and interpreted by modern television receivers. These properties include (1) having 262 or 263 total lines per frame, (2) the length between each HSYNC edge being constant from line to line, and (3) the length between each VSYNC edge being constant from frame to frame. #1 is important because although analog CSYNC was never standardized, both 262-line and 263-line progressive video are standardized in the digital CEA-861 timing specifications used for HDMI. Therefore, a modern digital display at least has a defined target digital destination it can map an incoming analog CSYNC source onto. #2 and #3 are vital because PLLs (phase locked loops) are used to regenerate the pixel clock by locking onto consistently occurring HSYNC and VSYNC edges. Any peculiarity in the position of the edges can cause the PLLs to lose lock and result in a “no signal” message, a “mode not supported” message, or a flickering screen. #2 and #3 are so important that they also apply to any input format, and aren’t exclusive to 240p.

A handful of the many possibilities for 240p CSYNC. All the flavors shown here adhere to the 3 critical timing rules discussed above.

A handful of the many possibilities for 240p CSYNC. All the flavors shown here adhere to the 3 critical timing rules discussed above.



Summary

The main takeaways from Part 1 are as follows:

1.) CSYNC is typically generated directly, and not from a combination of existing HSYNC and VSYNC signals.

2.) Many properties for proper CSYNC were established specifically for interlaced television broadcasting applications. These properties are now standardized and need to be followed today even if the original technical reasons are no longer relevant.

3.) 240p CSYNC, due to its similarity to 480i, has many variations which can easily confuse display devices.

4.) Adhering to the outlined critical timing specifications as strictly as possible greatly increases the chances that no issues arise when decoding CSYNC signals, regardless of input format (i.e. 240p, 480i, 480p, etc.).

Stay tuned for Part 2 where I’ll describe common CSYNC implementations derived from explicit HSYNC & VSYNC signals which don’t quite cut the mustard. These implementations break one or more of the timing properties established above.

References

  1. Benson, Blair, and Jerry Whitaker. Television Engineering Handbook: Featuring HDTV Systems. 2nd ed., McGraw-Hill, 1992.

  2. Jack, Keith. Video Demystified: A Handbook for the Digital Engineer. 4th ed., Newnes, 2005.

  3. Poynton, Charles. Digital Video and HDTV: Algorithms and Interfaces. Morgan Kaufmann Publishers, 2003.

  4. Consumer Electronics Association. "CEA-861-D." A DTV Profile for Uncompressed High Speed Digital Interfaces, June 2006.

  5. Electronic Industries Association. "EIA-170." Electrical Performance Standards - Monochrome Television Studio Facilities, Nov. 1957.

  6. Society of Motion Picture and Television Engineers. "SMPTE 170M-2004." Composite Analog Video Signal - NTSC for Studio Applications, Nov. 2004.

Posted
AuthorSte Kulov

Salutations, fellow ghosts and goblins! It's been awhile. And though we're sure you haven't missed us, we just reached a point where we're able to give you a decent status update. Here we go:

First, the main reason we've been quieter than usual is due to the fact that we moved out of the basement/dining room and into an actual office/lab space. It was a lot of time and work setting this up, but it has already paid off in streamlining our new development projects and how we operate in general. Those new development projects, including the Dreamcast YPbPr cables, are still in progress. No further updates about those just yet, but the mailing list will get an update as soon as we have something significant to share.

OK, we do have one small update on new projects. As of last month we officially became a licensed HDMI® Adopter, which means we can now legally design, manufacturer, and sell products using HDMI® technology. We're excited to be one of the first companies in the retro gaming/computing arena to be allowed to do this.

The factory just wrapped up a production order that contains Genesis YPbPr cables, SNES YPbPr cables, PlayStation adapters, 5x RCA Male-to-Male cables, and 5x RCA Extension cables. These will soon be on their way via ocean freight, and will take the usual unpredictable amount of time to get here. We will not be reopening our store right away when they arrive. In order to continue making progress on new projects, our store will remain closed for awhile longer. However, you will be able to purchase from the new shipment of products through distributors such as CastleMania Games and Retrostuff.ca. Please visit their websites for information/updates about what stock they'll have and when. CastleMania may be doing a pre-order system soon -- check with them for details.

When we eventually do reopen our own store, we will only be offering shipping to domestic (USA) customers. Selling internationally adds too much complexity and risk for us, making it much harder to continue doing things other than running a store. International customers can still purchase through the aforementioned distributors.

Lastly, we placed a couple of our more basic products on Amazon.com for sale and distribution. Depending on how well these sell on Amazon, we might consider posting more products there in the future.

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Have a very spooky October!

The terms HDMI and HDMI High-Definition Multimedia Interface, and the HDMI Logo are trademarks or registered trademarks of HDMI Licensing Administrator, Inc. LLC in the United States and other countries.

Posted
AuthorNickolaus Mueller

We have some important news to share, so please read on if you're interested in what we're doing. We appreciate the great response to all the products we've brought to market so far, with many of our items selling much faster than we anticipated. So... thank you for that! But as you might already know, that success has come with a lot of non-technical work that has taken up our time and prevented us from progressing in development on projects such as Dreamcast component cables and the HD-mizer.

With that in mind, we're going to be temporarily closing down the shop beginning July 1st. We're still moving forward with placing new orders for our existing products, but while those are getting manufactured, we need to focus our attention on getting development done. We'll of course share a reopening date to the mailing list when we have one.

If there's something you'd like to order directly from us, please do it by the end of June. Though our shop will be temporarily closed after that, Castlemania Games and Retrostuff.ca will remain open and *may* have stock of whatever you're looking for.

Thanks for all the support you've shown us over the years!

Ste & Nick

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Posted
AuthorNickolaus Mueller

Three quick updates for you today:

1) PS2/3 cables are back in stock. As in right now.

2) Despite our best efforts, we're getting a lot of emails inquiring about a Genesis cable restock. The answer right now is that we do not know when we'll have more. We're still working out forecasts for ourselves and with our distributors, and once we have those we'll be able to place an order and give people a better idea of a date. In short: no restock on our store for at least a few months.

3) Dreamcast YPbPr cables are still in development. Unfortunately, the project hasn't been worked on since before we restocked the store in March, due to being bogged down with non-stop sales and support issues during that period. That boring stuff has slowed down recently, so we're trying our best to pick back up our pending Dreamcast tasks within the next few weeks.

 

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Posted
AuthorNickolaus Mueller