Fallout 4 Gets Logic Gates, Is Functionally Complete

Fallout logic. This is literally called Fallout logic. This is far more confusing than it should be.
Fallout logic. This is literally called Fallout logic. This is far more confusing than it should be.

Fallout 4, the latest tale of post-apocalyptic tale of wasteland wanderers, got its latest DLC yesterday. This add-on, Contraptions Workshop, adds new objects and parts to Fallout 4‘s settlement-building workshop mechanic. This add-on brings more building pieces, elevators, and most importantly logic gates to Commonwealth settlements.

The Fallout logic gates are used in conjunction with electric generators, lights, and automated sentries used to build settlements. Although a simple NAND would do, there are several types of logic gates including AND, OR, XOR, NOT, NAND, NOR, and XNOR.

The in-game explanation for these gates is very, very weird. AND, OR, and XOR “transmit power or not depending on the combination of power to their inputs”. NOT, NAND, NOR, and XNOR are apparently different, “only transmitting power if their inputs are connected directly to the output of other logic gates”. The reason for this arbitrary distinction between different sets of gates is currently unknown except to a few programmers and project leaders at Bethesda. It should be noted {AND, OR, XOR} is not functionally complete.

With implementations of logic gates in video games comes some very interesting if useless applications. Already Fallout 4 has light boxes, allowing for huge animated billboardsFallout speakers, the wasteland’s equivalent of Minecraft’s note block, can be used to play simple melodies. You can do anything with a NAND, so we would expect automated, sequenced versions of animated billboards and monophonic synthesizers to appear in short order.

Functional completeness can add a lot to a game. Since Minecraft added redstone logic to the game, we’ve seen some very, very impressive block-based builds. The Minecraft CPU generally regarded as being the first, most complete CPU took about three months to design and build. This build didn’t use later additions to the redstone toolbox like repeaters, pistons, and the now-cheaty command blocks.

When Difference Matters: Differential Signaling

We have talked about a whole slew of logic and interconnect technologies including TTL, CMOS and assorted low voltage versions. All of these technologies have in common the fact that they are single-ended, i.e. the signal is measured as a “high” or “low” level above ground.

This is great for simple uses. But when you start talking about speed, distance, or both, the single ended solutions don’t look so good. To step in and carry the torch we have Differential Signalling. This is the “DS” in LVDS, just one of the common standards throughout industry. Let’s take a look at how differential signaling is different from single ended, and what that means for engineers and for users.

Single Ended

Collectively, standards like TTL, CMOS, and LVTTL are known as Single Ended technologies and they have in common some undesirable attributes, namely that ground noise directly affects the noise margin (the budget for how much noise is tolerable) as well as any induced noise measured to ground directly adds to the overall noise as well.

By making the voltage swing to greater voltages we can make the noise look smaller in proportion but at the expense of speed as it takes more time to make larger voltage swings, especially with the kind of capacitance and inductance we sometimes see.

Differential

diff4

Enter Differential Signaling where we use two conductor instead of one. A differential transmitter produces an inverted version of the signal and a non-inverted version and we measure the desired signal strictly between the two instead of to ground. Now ground noise doesn’t count (mostly) and noise induced onto both signal lines gets canceled as we only amplify the difference between the two, we do not amplify anything that is in common such as the noise.

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Spit Out VGA with Non-Programmable Logic Chips

It’s not uncommon to bitbang a protocol with a microcontroller in a pinch. I2C is frequently crunched from scratch, same with simple serial protocols, occasionally complex systems like Ethernet, and a whole host of other communication standards. But VGA gets pretty tricky because of the timing requirements, so it’s less common to bitbang. [Sven] completely threw caution to the wind. He didn’t just bitbang VGA on an Arduino, but he went one step further and configured an array of 7400 logic chips to output a VGA signal.

[Sven]’s project is in two parts. In part one, he discusses choosing a resolution and setting up the timing signal. He proceeds to output a simple(-ish) VGA signal that can be displayed on a monitor using a single gate. At that point only a red image was displayed, but getting signal lock from the monitor is a great proof of concept and [Sven] moved on to more intricate display tricks.

With the next iteration of the project [Sven] talks about adding in more circuitry to handle things like frame counting, geometry, and color. The graphics that are displayed were planned out in a simulator first, then used to design the 7400 chip configuration for that particular graphic display. It made us chuckle that [Sven] reports his monitor managed to survive this latest project!

We don’t remember seeing non-programmable integrated circuits used for VGA generation before. But bitbanging the signal on an Arduino or from an SD card slot is a great test of your ability to calculate and implement precise timings with an embedded system. Give it a try!

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How CMOS Works: MOSFETs, JFETs, IGFETS and More

CMOS opened the door for many if not most of the properties needed for today’s highly integrated circuits and low power portable and mobile devices. This really couldn’t happen until the speeds and current drive capabilities of CMOS caught up to the other technologies, but catch up they did.

Nowadays CMOS Small Scale Integration (SSI) logic families, I.E. the gates used in external logic, offer very fast speeds and high current drive capability as well as supporting the low voltages found in modern designs. Likewise the Very Large Scale Integration (VLSI) designs, or Very Very Large Scale if you like counting the letter V when talking, are possible due to low power dissipation as well as other factors.

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Gates to FPGAs: TTL Electrical Properties

On the path to exploring complex logic, let’s discuss the electrical properties that digital logic signals are comprised of. While there are many types of digital signals, here we are talking about the more common voltage based single-ended signals and not the dual-conductor based differential signals.

Simulated "Real Life"
Single-ended Logic Signal

I think of most logic as being in one of two major divisions as far as the technology used for today’s logic: Bipolar and CMOS. Bipolar is characterized by use of (non-insulated gate) transistors and most often associated with Transistor Transistor Logic (TTL) based logic levels. As CMOS technology came of age and got faster and became able to drive higher currents it began to augment or offer an alternative to bipolar logic families. This is especially true as power supply voltages dropped and the need for low power increased. We will talk more about CMOS in the next installment.

TTL was a result of a natural progression from the earlier Resistor Transistor Logic (RTL) and Diode Transistor Logic (DTL) technologies and the standards used by early TTL became the standard for a multitude of logic families to follow.

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From Gates to FPGA’s – Part 1: Basic Logic

It’s time to do a series on logic including things such as programmable logic, state machines, and the lesser known demons such as switching hazards. It is best to start at the beginning — but even experts will enjoy this refresher and might even learn a trick or two. I’ll start with logic symbols, alternate symbols, small Boolean truth tables and some oddball things that we can do with basic logic. The narrative version is found in the video, with a full reference laid out in the rest of this post.

Invert

1The most simple piece of logic is inversion; making a high change to low or a low change to high. Shown are a couple of ways to write an inversion including the ubiquitous “bubble” that we can apply almost anywhere to imply an inversion or a “True Low”. If it was a one it is now a zero, where it was a low it is now a high, and where it was true it is now untrue.

AND

2Moving on to the AND gate we see a simple truth table, also known as a Boolean Table, where it describes the function of “A AND B”. This is also our first opportunity to see the application of an alternate symbol. In this case a “low OR a low yields a low”

NAND

3Most if not all of the standard logic blocks come in an inverted form also such as the NAND gate shown here. The ability to invert logic functions is so useful in real life that I probably used at least three times the number of NAND gates as regular AND gates when doing medium or larger system design. The useful inversion can occur as spares or in line with the logic.

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Hackaday Prize Entry: A BeagleBone Logic Analyzer

If you have a BeagleBone, you already have a lot of tools. We’ve seen them used in driving hundreds of LEDs at a very high frame rate, used as a video card for ancient computers, and as a software defined radio. For his entry to The Hackaday Prize, [Kumar] turned his BeagleBone into a 14-channel, 100Msps logic analyzer that’s good enough to debug just about all those hobby electronics projects you’re working on.

The BeagleBone is only able to have this sort of performance as a logic analyzer because of its PRUs, those fancy peripherals that make the Beagle great at blinking pins really, really fast. [Kumar] is using both PRUs in the BeagleBone for this project. PRU1 reads from the input probes, and PRU0 writes all the samples into DDR memory directly. From there, the samples are off to kernel modules and apps, either sigrok, dd, or something you coded up in Python.

Compared to the cheap logic analyzers we have today like the Salae Logic and the DSLogic, [Kumar]’s project is just as good as any commercial offering (provided you can live with 14 channels instead of 16), and because it’s based on a BeagleBone, the software is infinitely expandable.

UPDATE: After this post was written but before it was published, [Kumar] finished up a blog post on how he’s building a logic analyzer with the BeagleBone’s PRUs. It’s a true tutorial, with enough code demos to allow anyone to build their own 8-bit analyzer on a BeagleBone, and there are more updates coming.


The 2015 Hackaday Prize is sponsored by: