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Analog signals are an important and very useful part of electricity in Survivalcraft. They further set SC ahead of other 'sandbox' games. The electricity component of Survivalcraft is the most advanced feature in all known sandbox games.


Digital -v- Analog Signals

A digital output can only be 2 values. Either it is a 0 or a 1. This is called a binary signal, since bi- means two. A 'pure' digital input is one that has a specific yes/no response and that means either it does something or it doesn't. The digital input also does not 'pass through' an analog value.  A lightbulb is an example of a pure digital input. All the inputs on an SR latch are pure digital. When an analog signal goes into a digital input, it will be treated as a 0 only if it is less than 0.8 Volts.

An analog signal in Survivalcraft can be any of 16 values. These values are 0 through 15. In many cases, they are called a voltage and that voltage is then 0 ~ 1.5 Volts. Notice that since we include the value 0, that counts as one of the 16 values.

Since analog has 16 possible values it is the same as a 4-bit digital bus. A bus is simply a group of related digital signals all going to the same places. It's 4-bits because that's how many digital lines (or bits) we need to show 16 different values.

The standard way of showing the 16 values of a 4-bit bus is called "HEXIDECIMAL". This literally translates to "six plus ten", or 16! Huh, figures. So a Survivalcraft analog analog signal can be called a hexidecimal signal, or hex for short. A chart showing the different ways we can write these values, is included at the end of this section.

The last column in the chart shows how an analog input will be treated when it goes into a digital input. Any value from '0' Hex to '7' Hex will be a 0 digital. Any value bigger will be treated as a 1 digital. If you look at the binary column and compare it to the "digital in" column, you can see that the "in" column is identical to the biggest bit - the one on the left - in the binary column. When the analog signal is read by a pure digital input, it is just a copy of the 4th bit on the bus.


Survivalcraft electrics use both types of signals but they can often be interchanged. A digital output of '0' is the same as an analog output of 0 Volts or '0' Hex. A digital output of 1 is the same as an analog output of 'F' Hex, NOT a '1' Hex, NOT a '8' Hex, either. A digital output has ALL the bits set (to 1). In effect, ALL signals are analog but digital outputs are limited to the two extremes and pure digital inputs only look at the high bit.



HEXIDECIMAL chart

This chart shows the different ways we can show the values of the analog signal. The voltage (decimal), binary and hex numbers in each row all mean the same number. They are just different ways to say the same thing. Binary shows the actual digital bits for that number. Hex is a shortcut way to write that number. Voltage is decimal which is just a way for humans to relate to that very same number. The "digital in" column shows what that value means to a pure digital input.


 Voltage     Binary     Hex   digital
(decimal)                      input
    0.0       0000       0       0
    0.1       0001       1       0
    0.2       0010       2       0
    0.3       0011       3       0
    0.4       0100       4       0
    0.5       0101       5       0
    0.6       0110       6       0
    0.7       0111       7       0
    0.8       1000       8       1
    0.9       1001       9       1
    1.0       1010       A       1
    1.1       1011       B       1
    1.2       1100       C       1
    1.3       1101       D       1
    1.4       1110       E       1
    1.5       1111       F       1




This is technical article and is not intended for the new beginner. You should already understand the basics of how the gates work before going any further.


Types of Analog Signals

The term 'analog signal' is actually a misnomer. The signals aren't quite what electrical engineers would call analog. They combine the properties of both a 'true' analog signal and a digital 'bus'. This bus carries the information of up to 4 digital bits. (This is commonly called a 'nibble'. A byte is 8 digits so 4 digits was named a nibble.)
The fact that they are actually 'hybrid' signals allows us to create some unique circuits that would be more complex otherwise. For the devices which do not actually take a real analog signal, it can be imagined that they have an implied A>D or D>A built into them.

They are most like a 'true' analog signal with these devices:

A>D and D>A converters, Battery, Hygrometer, Motion Detector, Photodiode, Pressure Plates, Target, Thermometer

They are hybrid signals with the following devices:

7-Segment Displays, Random Generator, Real Time Clock, Sound Generator

They are most like a digital bus with some devices:

4-LED, Memory Bank

The differences may only matter to the technically inclined:

If the 4-LED actually took a true analog signal, it would not respond in the manner which it does. Each LED reflects the state of one bit of the signal, rather than the signal level. If it responded to the level, it should have 16 LEDs instead. This does however, allow us to control all 4 LEDs separately with a single signal (bus).
The hybrid and bus type inputs or outputs may be considered to have built-in A>Ds on these inputs and D>As on the outputs.


Processing Analog Signals

Signal Propagation

The analog signal will propagate through the basic gates - as described below. These devces are:

AND, OR, XOR, NOT, DELAY

If the output signal is actually generated internal to a device, an analog input will NOT show through to the output. These types include:

4-Bit Counter, Memory Bank, SR Latch, Truth Table

Of course, an analog signal passes freely through wires and Wire-Through blocks.


Input Processing

When an analog signal (actually any signal) is input to a pass-through gate, the output is determined by the analog values of all inputs. The gates operate on a bit-to-bit basis. That means a NOT gate will invert each bit of the analog input. The AND, OR and XOR will perform their functions on each bit of the inputs individually. Say, in an OR gate, an input of "0110" (the 4-bit analog value) OR'd with the other input of "1001" would output a "1111". AND and XOR are done the same way.


The benefit of this shows when one input is analog and the other is pure digital.

In an AND gate, one digital input will act like a shutoff switch for an analog signal in the other input. Since a 0 digital is a "0000" analog, when you AND each bit you will get 0. When the digital input is 1, its analog value is "1111". If you AND that with the analog input you get the same value for the ouput. The output always represents the smaller of the inputs.
In an OR gate, the digital input acts like a 'shutON' switch. When there is a digital 1 on one input, the output will always be 1 or "1111" regardless of what the analog input is. When the digital input is 0, the output will be the same value as the analog input. The output is always the bigger of the inputs.
In a XOR gate, the digital input acts like a NOT gate that you can turn on and off. When the digital input is 1 or "1111", the output is the NOT of the analog input (each bit is inverted). When the digital input is 0, the output is the same as the analog input.

If both inputs are analog, the output is the function (AND OR XOR) done on each bit. This same process is done in every case.


If you run an analog signal into any other digital input, it will act like a digital signal. That means if it's less than '8' (or 0.8V) then it's treated as a 0. If it's '8' or higher, it's treated as a 1. A 'pure' digital input only looks at the first, highest bit.


The only known exceptions to this rule at this time are the Memory Bank clock input and the Sound Generator tone input. These are true hybrid inputs and actually serve two separate digital functions and depend on the hybrid nature of the Survivalcraft electric signals to accomplish that. See those pages for more details.

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