Back To Basics: HDMI

Posted under Back to Basics, Educational, Technology on August 18th, 2024 by

Today let’s talk about a technology we all interact with almost daily: HDMI. It stands for High-Definition Multimedia Interface and is currently the defacto digital interface for transmitting video and audio signals in a single cable. HDMI was first introduced in 2002 as an alternative to a popular standard at the time called DVI(Digital Visual Interface). It was developed by a group of companies including Sony, Philips, Toshiba, and Hitachi. The HDMI’s first version in 2002 supported 1080p video and 8-channel audio with 4.95Gbps bandwidth. The latest version(v2.1b) supports 8k@60fps and 4k@120fps with a bandwidth of 48Gbps.

Let’s discuss the electrical side.

An HDMI connector consists of 19 pins.
TMDS (Transition Minimized Differential Signaling) Channels (Pins 1-3, 7-9, 13-15): These are the three(D+, D- & Shield) pairs of main channels that carry video and audio data using differential signalling.
Clock(Pins 10-12): TMDS differential clock for synchronization between systems
CEC (Consumer Electronics Control) (Pin 13): This channel allows devices to send control commands to each other, like turning on your TV with your set-top box.
DDC (Display Data Channel) (Pins 15-16): Used for communication between the source and display. It’s I2C based. The display uses it to tell the source what modes/formats it supports.
Hot Plug Detect(Pin 19): Signals the source device when a display is connected/disconnected.

On the physical connector design side, there are 3 main versions. Type A Standard is the most common and biggest one, Type C Mini and Type D Micro are other smaller space-constrained versions. Pin count-wise all are the same except for size reduction. From the PCB routing POV, all the high-speed 4 differential pairs of TMDS signals are to be routed with a single-ended impedance of 50Ω and differential impedance of 100Ω.

HDMI has undoubtedly transformed how we connect our devices over the years. Personally, though I think, its future might be limited, especially with USB Type-C now supporting HDMI signals through Alternate Mode. Probably a decade away from USB Type-C becoming the universal connector for everything.

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The New Chip in Town: RP235X

Posted under DIY, Educational, Product Reviews, Technology on August 11th, 2024 by

If you’re in the embedded world, you’ve likely been swamped in the last 2 days about the new RP235X chip from Raspberry Pi, that is set to power the Pico2. Rather than putting a bunch of specs that everyone seems to be covering, I thought I would write about what I love about this chip and how it could be a game changer. For Specs, prices, and details check the attached images towards the end. It’s mostly self-explanatory.


I wrote about the first chip RP2040 from RPi some 3+ years back on how it was the most bang for buck chip out there at that time with ridiculously low prices and massive community support. RP2040 has proved beyond doubt its capabilities as of today. With the new RP235X, RPi seems to have outdone itself in making everything better and even keeping prices relatively similar(Not even accounting for inflation). It’s so audacious that they have put its manufacturing support at 20 years from now. I have not heard of any company backing support to their chips for 20yrs at launch. It’s ridiculous!

The most exciting part for me is the dual M33 chipset paired with dual RISC-V Hazard3 cores. Users can activate any two, even in combination(Not sure why though). This will single-handedly bring RISC-V support to a heck of a lot of software libraries from the community, potentially making RISC-V as close to mainstream as possible. I have a feeling that RPi is using this chip as a testbed for a future controller entirely in RISC-V. Heck, that will make the future chips potentially even cheaper with no ARM licensing.
I had 2 major cribs with the initial RP2040 while using them in my projects. One it always needed an external flash for storing programs, increasing footprint and BOM cost. The RP2354 series comes with a dedicated 2MB flash. Second was its poor sleep power consumption, they seem to have brought it down to a respectable 57uA@3.3V in the new chip.

All in all, RP235X is a worthing successor to RP2040 with more than double the performance. I think it will be the best chip in its price class. If you know of any other chips that even come close, let me know in the comments. What excites you most about this new chip?

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