advser hdmi 2 › ... › HDMI_Guide.pdf · A completely digital connection, HDMI offers 1080p high-deﬁ nition video and advanced audio connectivity over one cable. But questions

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This paper is an introduction to the installation and troubleshooting of HDMI.HDMI requires a completely new set of rules and different techniques in order for success.

The Installer’sGuide to

HDMI

CEPro Advantage Series • The Installer’s Guide to HDMI

By Jeff Boccaccio, principal, InVisions Technology

Sponsored by:

www.iavi.com

© 2008 EH Publishing.

CEPro Advantage Series • The Installer’s Guide to HDMI Sponsored by International Audio Visual, Inc. www.iavi.com i

SINCE ITS INTRODUCTION, HDMI has become one of the most talked about, popular and controversial cabling technologies to hit the market.

A completely digital connection, HDMI offers 1080p high-defi nition video and advanced audio connectivity over one cable. But questions concerning running it at long distances, reliability and

High-bandwidth Digital Content Protection (HDCP) have caused some custom installers to stick with analog cabling for their high-defi nition installations.

This paper is an introduction to the installation and troubleshooting of HDMI video. HDMI requires a completely new set of rules and different techniques in order for success.

CEPro Advantage SeriesThe Installers Guide to HDMIby Jeff Boccaccio

CEPro Advantage Series • The Installer’s Guide to HDMI Sponsored by International Audio Visual, Inc. www.iavi.com ii

Table of Contents

OverviewOverview 1

The HDMI Engine Video 2

Serial Intelligence 5

Supply Channel 5

CEC Channel 5

Video Bandwidth 6

Revisions, Revisions, Revisions 8

The Connector Everybody Loves 9

Ensuring Operability: Installation Scenarios Typical Source and Sink 11

The HDMI Receiver/Processor 13

HDMI Optional Switches 14

HDMI Distribution 16

HDMI Switching Matrix 17

Going Long DistanceFixed TMDS EQ 18

Adjustable TMDS EQ 19

Adaptive TMDS EQ 19

I2C Conditioner 19

CEPro Advantage Series • The Installer’s Guide to HDMI Sponsored by International Audio Visual, Inc. www.iavi.com iii

Anything But An HDMI CableCat 5 Converters 21

Coax Options 22

Fiber Optics 22

Wireless Technology 23

The Cat1 and Cat2 Cable Issues 23

Tools to Troubleshoot Symptom 1: No Picture 25

Symptom 2: Sparkles 25

Symptom 3: Flashes, No Audio, Pink Screen 26

Symptom 4: Picture Comes On, Then Goes Off 26

ConclusionConclusion 27

CE Pro Advantage Series: The Installer’s Guide to HDMITable of Contents

CEPro Advantage Series • The Installer’s Guide to HDMI Sponsored by International Audio Visual, Inc. www.iavi.com 1

Overview

I REMEMBER THE DAYS where it was common to offer the customer a bunch of free clear 18/2 speaker cable and having all the confi dence in the world that we had a fi rst rate installation. During that time, in the late 1960s and 1970s, high-end products were perfectly happy with these types of wiring schemes. However, as time trucked onward and new technologies surfaced, so did the need to improve our installation knowledge base of materials and techniques adapting to the new and improved systems.

Now, we are in the forefront of digital video and signal bandwidth is so large that we need to increase our skill level and knowledge base another notch in order to satisfy present and future technology.

This paper is an introduction to the installation and troubleshooting of HDMI video. HDMI requires a completely new set of rules and different techniques in order for success.

We will begin with a short tutorial of the HDMI system with a direct comparison to its analog counterpart. This will allow for a better understanding of the similarities of the two, while at the same time examining some of the major differences. With that you will get a better understanding of how and why the installation of these digital systems can be similar in some ways and different in others. We will also spend some time on all the Revisions to make that a little clearer.

From there we will discuss some steps to ensuring the operability of the system by way of cable management, as well as design limitations with countermeasures that can be harnessed to stretch some of these limitations that typically surface in the HDMI environment.

We will fi nish by covering some tools that can be used to troubleshoot a system both in hardware and in brain power -- the best tool of all.


The HDMI Engine

HDMI

HIGH-SPEED DIGITAL SIGNALING became part of our industry when it was obvious the analog alternative did not have the horsepower to support the growing demand for high-quality video.

We shall cover this in some detail so you have a good understanding of its complexity that yields its huge dynamic performance.

VideoBefore HD, life was much easier. Analog in nature, older systems had relatively low bandwidths compared to today’s HD systems that are almost 4 times greater. Besides the addition to color, the NTSC system has not had any signifi cant changes since the 1940s, when television made its debut in commercial applications.

In an effort to move beyond the dimension of the time, VCRs, and into more state of the art mass video storage, the DVD offered a form of medium that would not only revolutionize mass storage and quality capabilities but also allow for more modern chip-based cameras. It is possible to dump digital data directly into digital editing equipment to establish a master and then to disc production without having to go through any conversion process.

Today, all episodic features are now being shot with digital cameras. There is absolutely no analog production. Although many featured fi lms are in fact still shot with fi lm, all of these productions are converted to digital as soon as it comes out of the can. Signal data can now be edited and transferred directly to DVD or hard drives with little or no degeneration due to the digital to analog converters necessary for typical VHS tape and display monitors. We were now getting digital signaling directly from the DVD player only to end up converting it to analog in order for it to function on analog television sets. This was a bottleneck that one day would need to be rectifi ed.


Plasma and Liquid Crystal displays brought true, full digital signaling from input to screen with no analog conversion processes. Although analog converters still reside inside each machine for legacy products, the main thrust of each design is completely digital in nature.

There are many similarities between analog and digital video, however there are also some major differences to boot. We will walk through these one by one in an effort to use the similarities for reference as we move forward.

Figure 1: The HDMI Signal Confi guration

Figure 2: The Analog RGB Signal Confi guration

The HDMI Engine

HDMITransmitter

HDMIReceiver

EDIDROM

HDMI SOURCE HDMI SINK

The HDMI Signal Configuration

Video

Audio

Control & Status

Video

Audio

Control & Status

Data Display Channel (DDC)

CEC Line

Power

TMDS Channel 0 Red

TMDS Channel 1 Blue

TMDS Channel 2 Green

TMDS Clock Channel

HotPlug

Digital/Analog

Converter

Analog/Digital

Converter

VIDEO SOURCE VIDEO SINK

The Analog RGB Signal Configuration

Video Video

Audio Left

Audio Right

TMDS Channel 0 Red

TMDS Channel 1 Blue

TMDS Channel 2 Green

Vertical Sync

Horizontal Sync


Figure 1 and Figure 2 demonstrate the differences and similarities between each type of interface. While at a glance it may seem that the HDMI compliment may look a bit more complex than the analog version, it follows a simple rule my college chemistry professor kept beating over my head: “It is the same thing -- but different!”

You will notice that Figure 1 and Figure 2 both have three color channels (red, blue and green). The analog system has two sync channels and two audio channels, where the HDMI compliment has one clock channel, a supply voltage, a serial communication channel, a Hotplug detect, a CEC channel and no discrete audio channels.

The video channels supply the necessary video signal for the three basic colors. The only difference here is that the analog system transports this data in its original analog wave form similar to Figure 3 (below). This is what is known in our world as a “video envelope”. You will notice the sync tips negative in nature along with white video modulation taking up the largest part of the wave form. This waveform represents one horizontal line of information, for which there are 525 lines for each frame (actually 262.5 lines alternating even and odd frames.)

Figures 3 & 4: Video Envelope and TMDS Video Data

Figure 4 depicts a TMDS (Transition Minimized Digital Signaling) digital video data stream. You can easily see the huge difference between the two. Not only do they look different, but they transport audio and video completely differently. In the digital system, three separate data lines transport the massive amounts of digital video, audio and ancillary data. The audio is multiplexed with the video, eliminating

The HDMI Engine


the audio channels that were used in the analog system. One other major difference is that the serial data is transported along 100 ohm balance line cabling to improve signal to noise and establish a bit more output. The analog system uses 75ohm shielded coax in an unbalanced arrangement for the video portion and shielded wire for the audio.

Although many may believe that analog sync and the HDMI clock channel are similar in nature, they really aren’t. The analog systems’ sync tips are used to synchronize the horizontal and vertical operation, where with HDMI the clock channel is the gate keeper controlling the tons of data streaming from the Red, Green and Blue channels. All of

these packets of data need to be accurately and continuously aligned. One other tidbit of information that may interest you is that the clock channel’s speed is always one tenth the speed of the color channels.

Serial IntelligenceThe DDC, or Digital Display Control channel, is used between both sink and source, allowing for simple plug and play operation. Once the system starts up, this channel sends serial data back and forth in an effort to set the system for its best overall operational limits in both audio and video.

This channel also supplies all of the HDCP content protection keys. Without this data, the system will fail to come on. The HDCP, in most cases, has a 2 second life span and continues to demand refresh keys for continuous operation.

Supply ChannelThe supply channel is 5 volts and originates from the source. It is used to power the display system’s DDC communication circuitry in the event that the display is turned off. This way the source can align itself with the sink even if the sink is turned off.

CEC ChannelLast but not least is the CEC channel. Called the Consumer Electronics Control, it will supply us all with unifi ed control functions similar to the universal remotes we use today.

You will soon see more and more of this coming into operation from many of the major home entertainment fi rms.

The HDMI Engine


Video BandwidthVideo bandwidth has been talked about a lot lately because it has a direct infl uence on screen resolution, whether it is analog or digital. By enlarging the bandwidth we can move even more data. However, what many don’t understand is that in the digital space, it takes quite a bit more bandwidth to do the same job as analog. This is why you will see 20 MHz signal bandwidth numbers for analog 1080i and 1080p (this signal bandwidth refers to the analog Component Video Output), but in digital HDMI the signal bandwidth is different. The domain is a “square wave” data signal with 1s and 0s. Here there are 24 bits for each pixel in time that the clocking rates are at 75 MHz and 165 MHz for the same resolutions.

Remember that the actual data rates are for each color (Red, Green and Blue) are 10 times the clock rate. Add to that the more recent HDMI 1.3 bandwidth requirements that take it up to 340 MHz. When converting that to actual data that is transported on the (TMDS) BUS, these numbers skyrocket. For example, 165 MHz and 340 MHz can be compared to 1.65 GB and 3.4 GB respectfully (that is per RGB color).

When dealing with high-speed serial data such as in HDMI, every fraction of an inch difference in wire length can make or break a system. At 1080p, the data bit is approximately 600 ps (Pico seconds) or 600x10-9 seconds for a 1 or a 0. Designing these types of systems requires some forecasting to determine its application environment. Since we are dealing with sources, sinks and cables at a minimum, one must build in tight tolerance levels. This is in effort to alleviate any problems incurred from other devices that may have been sloppily installed. In general, in the manufacturing process, we allow about a 5% error factor which computes to no more than .160 inches @ 1080P.

That equates to about the thickness of a 2 nickels. Obviously this leaves a high probability of error between the conglomerations of circuit boards, twisted cables, interconnects, connectors, and electronic components. The odds increase even more when poor installations and long lengths are taken into account. These length differences are called inter and intra pair skew specifi cations. Inter pair skew compares the lengths from one channel to another

while intra pair skew compares lengths within each twisted pair.

As important as these timing issues are, so is good digital signal integrity. The dielectric loss (also known as loss tangent) of the insulation used in the actual twisted pair is critical. The higher the loss tangent, the more 1s and 0s get smeared and degraded as it passes through the length of wire.

But it is not measured the same way as in the old days of analog. It incorporates a system measurement known as Bit Transition Analysis or “Eye Patterns”

The HDMI Engine

Wire length differences are very critical.


The HDMI Engine

Figure 8: Eye Patterns

They are called eye patterns due to their resemblance of an eye when displayed. If there is one thing you must remember out of this entire paper, it is that eye patterns don’t lie.

The wave form in Figure 8 demonstrates an eye pattern with a digital data wave form shown in red and blue. What we look for in an eye pattern is for the data transitions that have decent symmetry and clear spacing between the signal and the eye mask (that solid blue hexagon in the center if eye diagram). These clearances are measured in percentage of the minimum specifi cation and are referred to as the Mask Margin. The higher the percentage, the further away the eye is away from the mask.

The mask size was determined as a minimum area to guarantee the signal integrity. It varies with different video data rates (a 720p mask is different than the 1080p mask) and, represents the minimum specifi cation as set by HDMI. The name of the game is to produce a robust and symmetric eye around the eye mask, keeping any signal data as far away from the eye mask as possible to achieve the highest Mask Margin percentage. Touching the mask, called “Kissing the Dirt,” is where bit errors can begin to occur and cause the sporadic “sparkles” on the screen. The eye on the left of Figure 8 has a clean and robust pattern measuring 40% margin compared to the one on the right, which has closure, specifi cally on the leading edge, dropping the margin to 1%. This is due to signal degradation within the cable, source or sink.


Revisions, Revisions, RevisionsAfter HDMI Rev 1.1, not much had changed until Rev 1.3 was released. The major difference between Rev 1.3 and its predecessors is bandwidth. As I have already mentioned, the data bandwidth required for Rev 1.0 was 1.65 GB per channel. Rev 1.3 increased that bandwidth to a whopping 3.4 GB.

Always remember when referring to bandwidth that 3.4 GB is for each channel. Three channels put together total 10.2 GB. In the real world, what this means is that HDMI has allowed us more space to move things. You must think of the HDMI interface as a conduit or pipe that moves data. The faster the pipe, the more data you can ram down it. With the extended bandwidth we have more room for more optional goodies we can add to the interface. Better color, more audio protocols and even better frame rates are possible.

One of the great attributes of HDMI is its expandability and its backward compatible nature when working with legacy Revisions. Figure 9 defi nes all the Revisions.

Figure 9: HDMI Revisions

The HDMI Engine

Max Sig 165MhzMax TMDS 4.95GB/sMax Video BW 3.96GB/sResolution @24bits 1920x1080p60RGB and YCbCrColor Depth 24 bits per pixel8 Channel/192kHz/24-bit AudioBlu-ray/HD-DVD

Rev 1, 1.1, 1.2

5GB

/s

Max Sig 340MhzMax TMDS 10.2GB/sMax Video BW 8.16GB/sResolution @24bits 2560x1600p60Color Depth 48 bits per pixelAuto Lip SyncDVD-A SACS, TrueHD, DTS-HD

Rev 1.3, 1.3a, 1.3b

10G

B/s


The Connector Everybody Loves Now that you understand more of the critical features of the interface, you may have a little more respect for the work that was introduced into the connector.

The male connector typically mounted on the circuit boards is constructed very similar to a USB connector.

Figure 10: The male HDMI connector

The pins are designed to connect to its female counterpart by sliding on to one another. This technique offers a straight shot for data to fl ow. As critical as timing differences may be, so is the path of which the data rides on. The object is to maintain constant impedance and minimize signal refl ections as much as possible. Moving high speed data around tight corners can degrade its integrity. It is like driving a race car through hair pin turns. The faster you go, the more tendencies the car will have going straight off the road rather than making the turn. Balanced line circuit board traces, connectors, and wire must keep their transitions at a minimum and under control

Although many don’t want to admit it, the HDMI interface was never designed to go miles in wire length. Nor was there any intention for using wires that look like a garden hoses. It was designed for much thinner cable, lighter in weight allowing the locking springs in the connector to successfully hold the connector in place. In reality, this is not the case. In an effort to move data further, an increase

The HDMI Engine


in wire gauge provides the necessary cross sectional area dimension to support high data rates with distance. The only problem is that the weight of the cable pulls the connector out. Never heard of a USB connector falling out, did you?

It is what it is and there is not much we can do about that now except adapt our installations to refl ect an issue like this. We will cover this a little more later on.

The supply power on the bus is positioned on pin 18 of the HDMI connector. I want to bring this to your attention because this particular pin is set back about 50% in the connector. It was done this way so that all the data lines, DDC lines, CEC lines, Hot Plug Detect, and grounds are all connected fi rst before the power is turned on. So if the connector comes out just a little bit -- well I guess you can fi gure that out!

The HDMI Engine


Ensuring Operability: Installation Scenarios

THIS IS WHERE THE FUN BEGINS. We need to fi nd the correct products to provide a reliable and operational system using HDMI as the audio and video interface. Now you have to plan each installation carefully, not only in layout but in hardware. Since there are so many different confi gurations of system topologies, I will try to cover some common design models.

All the information that will be presented here is from real life experiences both in the fi eld and in our lab. We are continually bringing in products and scenarios from the fi eld to troubleshoot and rectify issues that may cause problems. We now have an extensive database of tests and procedures of which much of this data has come from.

Typical Source and SinkFigure 11 (below) shows the most common system arrangement. One or two sources can be used in conjunction with a display (sink) that has multiple HDMI inputs. If the two units are relatively close to one another, the possibility of a problem drops considerably. The one thing to always remember is the overall Margin of Headroom for the system.

Figure 11: Source-to-sink system arrangement


The Margin of Headroom is the performance level over and above the minimum HDMI specifi cation, which not only includes eye patterns but also DDC, timing and power. You need all of it! Whether you are using a 1 meter or 3 meter cable for short runs, keep thinking Headroom. By using this tool you will fi nd yourself in a far better position if you do run into problems. Troubleshooting becomes much easier when you know you have plenty of Headroom Margin.

Another important detail to watch for is the fl exibility of the cable you are installing. Remember that the connector was never designed for some of these larger cable products now available. So if you have a stiff cable that does not like to bend a lot, you may fi nd it pulling out of the connector. If the display or the source has limited room behind for the connector to form a decent radius, a cable will have a very hard time staying connected. Conversely, you don’t want to have tight 90º kinks in the cable, otherwise you may start to degrade data from the severity of the bend.

Figure 12: HDMI cable fl exibilityAlways remember that any time you add anything to the interface, it will usually affect its Margin of Headroom. The key is to start with as much Headroom Margin as you can possibly squeeze out of the system. This will always give you a far better chance for a perfect operating system.


Max 90mm

Plug

Receptacle

Very Important


Figure 13: HDMI receiver/processor setup

The HDMI Receiver/ProcessorAs HDMI became more popular, so did the need to switch to multiple HDMI inputs. Since most of these systems require a surround processing system, it was only natural for audio processors to offer HDMI switching. Having HDMI switching within the processor allows for much more fl exibility as a central control processor. Now audio with an assortment of audio processing is provided along with video both with HDMI and analog video with format conversion circuitry, making life very easy for the end user. This, however, does not come cheap. In order for these companies to provide such a piece requires these fi rms to install HDMI receiver chips and HDMI transmitter chips to the circuitry.

As HDMI data is received, it is de-serialized into standard RGB or YCrCb digital data. This is where all the goodies get put in. Here, an on screen display (GUI) can be inserted. Scaling, color management and video conversion processing can also be added. There are also ports on these parts for audio insertion and extraction.



Figure 14: HDMI receiver and transmitter chips are necessary

One key advantage to units with HDMI receiver/transmitter pairs is that it basically resets the BUS by re-clocking the data and restoring the original output levels and integrity.

HDMI Optional SwitchesHere is a perfect example why you should have as much Headroom Margin as possible. Many HDMI switches are nothing but a Mux system. A Mux is nothing more than a chip set that has multiple inputs or outputs or both. They do not replicate an actual HDMI transmitter or receiver. The likelihood for these types of products to have anything close to unity gain is unlikely. Just by adding another connector to the signal path immediately introduces losses. These losses can be made up by signal processing and a gain stage, depending on the way the product was engineered. Most inexpensive switch systems do not have good signal processing and will have some losses in the process.

We have even experienced products with large signal level differences between inputs. Eye patterns were measured between each input and the output, with some inputs being much better than others. Each input has to come into these products from different locations in the chassis. The chip inside is positioned to one side and the traces on the printed circuit board are not the same length, which caused the different performance. That means that printed circuit board designs become crucial to the overall integrity of the switch. Moving data over several inches of printed circuit board material can be a challenge -- not to mention making any turns on the board


HDMIReceiver

HDMITransmitter

FPGAFPGAOSD,

Scaling, etc.

HD

MI IN

AUDIO OUT AUDIO IN

HD

MI O

UT


Figure 15: Circuit Board

This requires an experienced and savvy PCB engineer to be successful. The rules of engagement are the same whether we are inside the hardware or connecting to it. This is why I cannot stress enough to begin with plenty of Headroom Margin. The HDMI system was designed to work under real life conditions with losses taken into consideration up to a point. Too much wire, sloppy wire management and low quality products can and will sting you if you let it. Keep it short and as direct as possible. If you need to make a corner, loop the cable once similar to Figure 16 (below).

The DDC channel can also become an issue here. We are now sharing the crucial plug and play data between multiple sources. There is nothing wrong with that, but we have found instances where an accumulation of stray loading capacitance can affect the integrity of the rise time necessary for lossless data to communicate.

We will cover more of this when we get to problem solving.



HDMI DistributionHDMI distribution is becoming more popular in the design of homes and commercial systems. Many of the rules we have covered in the switch section comply with distribution except for one major point. Most of the displays that we are connecting to this product are in different locations. Some close, some far away. As in the inexpensive switches with input differences, we have found distribution systems with output differences. This can actually become a bigger issue compared to a switch.

In our experience measuring these products, we have found some have differences between outputs with no rhyme or reason. Output 1 may be better than output 3 but output 2 is worse than output 3.

Figure 17: Output devices and quality loss

If you are positioning the unit at the front end of the system where most would reside and connect the furthest display to the worst output channel, you may fi nd yourself with no picture, lots of sparkles or intermittent fl ashes of brightness. Be careful not to draw a conclusion on just one fi nding. Just by moving that particular display to another output port with better integrity can solve the problem. Again, I cannot stress enough the need for all equipment in the system to have reasonable margins over the HDMI minimum requirements. It will always pay big dividends at the end of the day.

DistributionDevice

Loses due to PCB board integrity

LOSS

LOSS

LOSS

LOSS

LOSS

LOSS

LOSS



HDMI Switching MatrixThis has been a long time need in the industry. Matrix devices are used to operate multiple displays with multiple sources. This is no doubt the most complex of any HDMI device. Now both input and output devices have to be routed throughout a switching matrix that encompasses 12 different bus lines both on the input side and output side of these parts. So every input and output requires a minimum of 24 board traces.

With a typical 4x4 matrix, 96 traces would have to be systematically routed on the PCB and still stay inside all the dimensional restrictions. Plus, at least with better quality products, each input and each output uses HDMI transmitters and receivers that provide all the benefi ts we described in the receiver section.



Going Long Distances

IF I HAD A DIME for every time someone asked me about this. Long haul operation has no doubt been one of the most popular requests from everyone in the industry. It’s kind of ironic since it is the one thing that

the HDMI design did not really support from the start. But by way of new technology, we now have products that do in fact offer a means to carry HDMI over very long distances. Just remember the same rules apply.

The products that have solved many distance issues are equalizers (EQ). Usually positioned on the sink side of the system, these products can clean up video data and allow for normal operation. There are many different designs that are available. We will cover these individually.

Fixed TMDS EQFixed equalizers are devices set for a particular amount of correction. When we say TMDS EQ, we mean just the video and audio part of the HDMI link. TMDS is the acronym for Transition Minimized Digital Signaling, which refers to the high-speed signal data. These products work very well, provided that you match the fi xed performance to the length or integrity of cable you are using.

Some of these units may have information accompanying the unit that describes its parameters. You must pay attention to this. If you are going 30 meters and the device is only set for 20 meters, you may not be able to pull this one out. One major rule to follow is to always use an EQ device that has its own power supply. These units can really pull some serious current. If they use the 5 volts power on the HDMI bus, it may pull it down so far the system will fail to operate. The resistance of the cable or the 5 volt current capability of the HDMI Source may limit performance.


Adjustable TMDS EQAdjustable equalizers perform very well provided you use a tool to adjust them correctly. We have found some models that are adjustable but without any access hole to adjust it with. Go fi gure. Here, the user would install the unit and basically view the display for operation. But be careful. You may fi nd yourself increasing EQ to a level that is adequate for the display with no visible sign of operation.

We have seen this on some displays where the receive processor has timed out. Just by restarting the system, the unit will respond to the new EQ levels. Keep increasing the EQ until you start getting any abnormal artifacts upon restart. If you do, just back it off a bit and let it be. Whenever you make a correction to any HDMI system and get negative results, always try restarting the system before you start pulling your hair out.

Adaptive TMDS EQThis type of equalizer is for the no-brainer installation. The term “adaptive” means just what it says: the device adapts itself to the required needs of the interface. Usually found on the sink side of the system, the Adaptive EQ will automatically adjust itself and adapt to the necessary EQ required to correct for any defi ciencies in the system.

One nice thing about this is that if you have sources with different integrities, the adaptive EQ will correct for these on the fl y, usually offering a seamless change without the user ever seeing the change occur.

I2C ConditionerMany calls we get about HDMI issues have nothing to do with the high-speed video at all. Just because the system is not functioning does not mean it is related to the video data. In fact, the majority of the problems we see are not video related at all. Instead it is because of issues such as I2C.

This is the serial protocol used on the DDC line for EDID (Plug and Play) and HDCP. There are specifi c specifi cations for this data recovery. Although it is much slower in speed (about 100KHz for HDMI), it is very susceptible to stray capacitance issues on the BUS. It can come from connectors, cables or anything that the BUS is connected to. If the capacitance level gets to a critical point, it will slow the rise time needed for proper communication.



Figure 18: Normal and slow rise times

You can see by this illustration that the A wave form has very little delay in the beginning while the B waveform has a much greater delay. The green box in the middle is the location the data is taken from. Once you start breaching this green area, your communication channel can get all messed up. Failures such as no audio, no picture, pink screen or fl ashing are just some of the problems that can occur with a failure due to DDC I2C integrity.

You may fi nd that some cables in a system like this may work while others do not. It has absolutely nothing to do with the high-speed data lines. In fact, the video can be perfect and have excellent mask margin percentage numbers, but if the DDC line has larger rise-time issues the unit will not pass HDCP and no picture will be displayed. We have seen high-quality products used that failed and lower quality products perform fi ne in the same system. The reason for this is that while the higher-quality product had a beautiful mask margin, it also had a below-average capacitance on the DDC line. The lower quality product did not have the margin that the better cable had but had a lower capacitance on the DDC line. Although the margin was low, it was enough over the minimums HDMI requirement, so it passes the video.

Remember, DDC failure comes from the accumulation of capacitance from all the parts that make up the system. It does not mean the high-quality cable is bad. It just means that, when used with particular sources and sinks with higher capacitance, it may fail.

There are now conditioners available that will correct these DDC issues so well that they can raise the allowable system capacitance by almost 100 times. In most cases, they encode/decode type systems that require units on both the source and sink side.



Anything But an HDMI Cable

Cat 5 ConvertersIt’s not like we have to use HDMI cables any more. There are now some terrifi c devices that are on the market that employ a form of EQ specifi c for other 100 Ohm cables such as Cat 5.

Figure 19: HDMI and Cat5 Connections

These are products that incorporate two Cat 5 cables for the entire HDMI interface. One nice feature of Cat 5 is that they use RJ 45 connectors that can easily be installed in the fi eld. The conversion is accomplished at the source side and then converted back on the sink. Since there are electronics used in both the transmit side and the receive side, you will see products come through with a power supply for both devices. There are still others that have solved this problem with just one supply running the entire system. They still fall prone, however, to all the HDMI rules we have discussed, including DDC issues.


But there are inline conditioners that can be installed that will rectify the problem, and there are others that have the conditioner built inside the Cat 5 converting system. This completely rectifi es the issue whether it is needed or not, and makes good sense, in my opinion.

Coax OptionsStill more products are becoming available that will operate HDMI over multiple RGB Coax lines.

These offer very high integrity levels for 1.2 systems as well as 1.3 high speed products. Again, these products should be investigated on your part to see if they offer any DDC line conditioning. Like I said before, you can have all the high-speed data bandwidth in the world, but without DDC, you’re dead in the water.

Figure 19: HDMI and Coax Connections

Fiber OpticsFiber has been somewhat of a sleeper. Although it is most defi nitely the best form of data transportation, it just did not seem to hit any kind of real use.

There are two reasons why this has occurred. The fi rst has been the problem with termination. Fiber Optic connectors are as diffi cult to put on in the fi eld (perhaps not as bad) as there would be with HDMI. The second reason is most defi nitely cost. Not until recently has the cost of these products been anywhere near competing cable systems. Now with some of the latest equalizers, DDC conditioners and better cable products, the need for fi ber still has a ways to go.



Wireless TechnologySince some of these newer wireless technologies have just recently hit the streets, we do not have a tremendous amount of data for them. There are some direct benefi ts to wireless. Provided that the wireless system is stable enough for continuous operation, the system seems to perform quite well.

The only drawback with the fi rst launch of these products is that they use of some type of video compression, which is opposite what the HDMI uncompressed system was intended for. However, there may be newer products popping up that do claim an uncompressed (or at least minor compression) of the video data. If it works and you’re happy with the results, then go for it!

The Cat1 and Cat2 Cable IssuesSince the release of Rev 1.3 and its forecast to provide data rates as high as 3.4 GB/s, it again brings to the table the capability of products that can handle these extreme bandwidths. Hardware that is rated as 1.3 must pass HDMI 1.3 minimums. The same goes for cable. If you intend on using any 1.3 hardware, you should be using cable that is Cat 2 Rated. These cable products are designed specifi cally for the higher data rates that can come from 1.3 hardware.

Due to the challenge for cable to be able to pass these extreme data rates, all 1.3 receiver products have internal EQ that provides an extra boost of support. This boost is only for TMDS data, not DDC data. Again, think Headroom when selecting these products. Remember that Headroom is the performance level of the entire interface over and above the HDMI minimums.

Look for these values: ■ Mask Margin

■ Inter Pair Skew (Timing)

■ Intra Pair Skew (Timing)

■ DDC Rise Time

■ Power Supply



Tools to Troubleshoot

WHEN YOU NEED TO troubleshoot, the best tool of all is the old noggin. Once you have a solid understanding of the system, troubleshooting becomes pretty easy. Tools such as deductive

reasoning become exercised quite a bit. Let’s run through a few scenarios to give you an example of how you may use your brain.

Typical source and displays will be the easiest to work with. The method is pretty much the same even when the system gets bigger. Remember the rule “It is the same thing -- but different!”

Try to start with some good habits. One very important habit is to use good products. Try building an inventory database of known products that have worked in the past or product mixes that you have tried in the shop. Continue to strive for as much Headroom Margin as possible. Just because you had success with a cable connected to a particular DVD player and display does not necessarily mean that that cable will work with every other setup out there. You must always keep in mind the aggregate of the system. Keep these confi gurations in some kind of order so you can pick and choose products quickly for each job.

If you have a job that is complex and requires high data demands, don’t skimp and purchase low quality products. Research these products by manufacturer and check the specifi cations. Most of the better fi rms will go out of their way to provide you with all the data you need to determine their products performance. Check for eye pattern mask margin percentage, skew timing and DDC rise time numbers. If they can’t get you the numbers, look at the waveform and take a rough guess how far the eye is away from the mask. This will at least lead you to some reasonable answers. Check for a fl exible and well made cable. Make sure it has a strong outer mold for the connector. You may fi nd some with rubber molds and others with metal housings.


Another standard procedure is to stage the system before it goes out. Make sure all the peripherals work well with one another with the type of cabling you intend on using. Even though the system should perform with good products and installation techniques, it never beats testing the system before it goes out the door.

Symptom 1: No PictureShut everything down, then restart the system with all the connections in place. Watch the screen. If you see a notifi cation of resolution (this is a function of either the sink, source or both and may not be available on all equipment) chances are the DDC line has communicated between source and sink. This is good!

The problem is probably video related. If you are using an active product like a cable box or satellite box, try using a DVD player. Many times the player comes on with the brand’s logo showing. If the picture goes off when you think the program material should have started, it could be that the HDCP is not getting the proper key. This can be a cable issue or a hardware compatibility issue. Remember that the HDCP keys are transferred using the DDC line on the cable. The most likely culprit is the cable.

First, try a shorter cable if possible, or try another cable brand. It might be that another brand has less capacitance in the DDC line. Another possibility is that the internal capacitance of either the source or sink is on the high side of the allowable capacitance limit. In that case, you can swap out the source and/or display to see if a different confi guration solves the problem.

Symptom 2: SparklesUsually more noticeable on black areas, sparkles tell you that you have a video data transmission problem. If you were to view this signal on eye pattern test equipment, you would see the signal encroaching on and probably violating the mask, causing lots of bit errors. In most cases this is cable related. It could be just that the cable is not performing very well due to its length. Shortening will improve the integrity greatly. You could also try to add a cable EQ to the system.

Remember that, in most cases, the product has to be located at the very end before it enters the sink. This goes for displays and switching (see fi gure 20).



Symptom 3: Flashes, No Audio, Pink ScreenThis is usually caused from a bad DDC line not communicating properly. It can be time consuming because you have to basically eliminate all the good things to fi nd the bad.

First, power up the system while all the HDMI cables are connected. Then, if you can, try the products with shorter cables. Here you need to see if the system works at all. Hopefully you have tried all these products before they were delivered to the sight.

If for some reason the system still fails to come on, start using different inputs. You may fi nd that your cable box will work and your DVD may not or vice versa. This can happen because of stray capacitance on the DDC line. This stray capacitance may be inherent in the hardware itself. If you think that this is the problem, try getting a DDC line conditioner. We have seen these types of problems completely go away when conditioning is introduced.

Symptom 4: Picture Comes On, Then Goes OffThis is a common one. In most cases, it is one of two things. If one or more of the video TMDS channels has a high bit error rate or is not working at all, you’ll have this problem, Many times it may come back with tear lines through it. It all depends on the display and how it reacts to the lack of complete data. The second case is the DDC line is just not quite making it and HDCP is not getting a new refresh key. Here, replace the cable or make it shorter. If all else fails, try conditioning.

There are some tools now coming out that can also assist in solving some of these problems. There are cable testers that will at least check the cable for continuity. Remember that this is not an eye pattern tester. This is simply a continuity checker. There is a lot going on inside these cables. Some have multiple grounds while others do not. There are also balance lines that add up to the 19 connections. Check these before you go to the sight.

There are also some testers with status LEDs for power, hotplug detect, and DDC lines. These can be very useful in the fi eld.

I know of more products on the horizon that will be available to give you a complete status report on the systems bus.



Conclusion

IF YOU KEEP THE BASIC RULES IN LINE, you will have a very good chance of solving many of the issues that seem to crop up out in the fi eld. Think digital and work through all the different combinations of the interface. Keep in mind how things happen and when.

With time, you will get much better at it.


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