Using Allion’s AJSC-1 EDID/SCDC Controller to Test HDMI Source Devices

AJSC-1 EDID/SCDC Controller is a neat test tool developed by Allion HDMI test engineers to control and emulate EDID and SCDC registers in HDMI devices. Its main purpose is to help control and encourage HDMI devices to output certain signal or to move to a desired state when testing.

With its small form factor, AJSC-1 is highly mobile and can fit in any test environment imaginable.

Introducing AJSC-1 in your HDMI test lab can save test engineers more time as it would shorten setup time, and if needed debugging time, considerably.

With the addition of SCDC register controller and emulator function to the existing HDMI EDID emulator, testers can now use AJSC-1 to help execute just about any HDMI electrical tests.

AJSC-1 has the following main functions:

  • EDID emulator and EDID editing functions
  • SCDC emulator and controller
  • Can emulate and control +5V Power / HPD pins
  • Can execute some HDMI 2.1 Compliance Test Items
  • DDC Transactions Monitoring Function

By using AJSC-1, testers can greatly improve test efficiency with regards to test time and accuracy.

As an example of how neat and useful AJSC-1 can be, we’ll show you how to execute HDMI Source device’s electrical tests using AJSC-1.

For this demo, we prepared a PC with AMD’s RX580 GPU installed. We want to measure this GPU’s HDMI eye characteristics while outputting 3840 x 2160 60P RGB 4:4:4 24bit.

Connecting the DUT(device under test) to the oscilloscope

We used HDMI test fixture (test point adapter) made by Wilder Technologies to connect the source device to the oscilloscope.

We connected the HDMI’s TMDS clock and data pairs to the oscilloscope probes since that’s where we want to get our eye diagram from. However, for the control pins such as the DDC pair, HPD, and +5V Power,  we will connect these pins to AJSC-1 (see below).

As for the other TMDS data pairs that are not being tested at the moment, they need to be terminated with 3.3volts. To terminate this TMDS data pairs, we use Allion’s HDMI Load Board (see below).

EDID settings and DUT’s output signal

Next, to make the source device (the PC) output 3840 x 2160 video format, we need to configure the AJSC-1’s EDID settings. The VIC(video identification code)for 3840 x 2160 60P 16:9 is 97 so the video format is assigned the same number in the AJSC-1’s GUI.

As you can see in the GUI below, when you choose EDID_4k_6G in the EDID dropdown and VIC97 in the VIC dropdown and click [Set EDID] button, the EDID content will be updated and HPD pulse will automatically be sent to the source DUT.

At 4K60p 24bit output, when the signal data rate goes above 3.4Gbps per lane,  the source must scramble its TMDS signal and it must change the data to clock ratio from 10:1 to 40:1.

The source DUT must signal this condition (to the sink) by writing the information to AJSC-1’s (acting as sink) internal SCDC registers. When this happens, [SCRMB] and [CR:1/40] indicators in the GUI below will turn active green.

Quickly checking the TMDS clock and data being outputted with an oscilloscope, you can confirm that 5.94Gbps (4K 60P RGB 24bit bitrate) signal is being registered (see below).

( Yellow: TMDS Clock+, Green: TMDS Data0+, Blue: TMDS Clock-, Red: TMDS Data0-)

After confirming that the DUT is outputting the desired signal, we can now proceed to execute the eye diagram test. The resulting HDMI signal eye diagram can be seen below.

Since the signal waveform below does not touch the specified eye mask, we could say that the DUT passed the eye diagram test.

By using the AJSC-1 this way, HDMI testers could easily output various signals (like 4K 60P) for testing. Of course, depending on the source DUT you want to test, you can use different EDID and/or VIC settings to encourage the source to output the desired signal.

Although we used Keysight’s oscilloscope for this demo, Allion also has Tektronix scopes that can execute similar tests.

Changing and checking EDID is easy with AJSC-1

HDMI source compliance test requires getting signal eye diagrams in various clock/data rates. For example:  480p60(27MHz), 1080i(74.25MHz), 4K2Kp24(297MHz), etc. However, for some HDMI source devices out there users cannot manually select what signal the source should output. These sources instead use the EDID information found in sink devices (e.g. TVs) to automatically decide what video format to output.

When testing this kind of source devices, the usual practice was to change the EDID EEPROM used in the test point adapter everytime you want to test different resolution or data rates. This procedure is very time consuming and if the desired video format could not be outputted, you will still need to edit the EEPROM’s EDID data anyway.

With AJSC-1, changing EDID through the use of a special application is very easy.

AJSC-1 includes standard EDIDs that can be invoked easily and they will be good enough for most testing occasions. If for some reason the source needs special EDID to output the desired data rate or video format, AJSC-1 can import/export EDID binary data that can then be applied to AJSC-1’s EDID emulator.

Other than binary formats, AJSC-1 also supports other EDID formats such as Teledyne LeCroy’s (Quantum Data) xml format.Moreover, AJSC-1 has now added its own EDID editor which will enable testers to confirm and edit EDIDs on the fly. With these EDID editing and emulating functions, testers will now have in their arsenal all the necessary techniques on how to easily force the source to output the desired video signal.

One more thing…FRL support!

We’re very excited to announce that AJSC-1 now supports HDMI 2.1’s new FRL(Fixed Rate Link) function. Please see AJSC-1’s new GUI for FRL control.

We are still testing this new AJSC-1 FRL control feature and are actively working with third party equipment makers to automate the FRL control function. We will give you an update when we got new developments about the new FRL function. Just remember that you heard it from us first. ^^;

*This is an English rewrite of a previous article posted in Japanese:
Allion AJSC-1 SCDC/EDIDコントローラを使用したHDMIソース機器の測定
We figured there are also many HDMI engineers outside Japan who would want to get a hold of AJSC-1 — small, versatile, and useful as it is. ^^

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