Description (From Recipaedia )
Writeable memory bank containing 256 4-bit words. The memory can be addressed using two 4-bit address lines placed on the left and right. If an address line is not connected, it's assumed to be zero. Value stored in the memory bank under the specified address can be read at the top output. Bottom input is used as a clock in a similar fashion to SR latch. If the clock line is not connected, reads are immediate. To write to the memory bank, supply the value to be written on the back input (you must use wire-through-block). The write is triggered by setting clock input to a low voltage between 0.1 and 0.7 volts (a value of 0.8 and larger will trigger a read). The contents of memory block can be manually edited by tapping edit button when block is held in hand (see warning below) or looked at. Can be placed on any surface and rotated to desired orientation.
Connections
There are a total of 5 connections to the memory. The output is on 'top' and the two address signals are on the 'sides' - the least significant to the single dot and the most significant to the double dots. The clock input goes in where the arrow or dart is, on the 'bottom' and the data input is through the back.
Crafting
Crafting requires 6 germanium crystals and 1 copper ingot. You get 4 Memory Banks.
Understanding It
You can think of the memory like a big BINGO card, or Battleships playing field. "G-4" defines one location in either game. The letters would come from one address line while the numbers come from the other one. The memory bank is a much bigger card than that:
||0 1 2 3 4 5 6 7 8 9 A B C D E F| 0||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 1||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 2||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 3||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 4||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 5||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 6||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 7||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 8||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| 9||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| A||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| B||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| C||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| D||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| E||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X| F||X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|X|
This table is the same as you will get when manually editing the memory. The numbers across the top represent all the analog values for the low address (one dot). The numbers down the side represent all the analog values for the high address (two dots). The spot where the two lines cross is the location you can read from.
When you put any value on the address inputs, the memory finds the location where those addresses cross. It copies the data (X) from that location to the output.
If you connect the clock input to anything, the memory will wait to copy that data.
Any one address can also be programmed electrically. Writing to the memory is quite complex and is best to be avoided when possible.
How to Use It
Addressing
You can only access a single location in the bank at a time. Only one of the X's in the chart above. You need two signals to find one X. Why two? Because each signal in Survivalcraft can represent 4 bits, or 0 to 15 (analog 0 to F). The chart makes it easier to see.
The inputs on left and right of the chip are the two address lines. The one with a single dot sets the 4 low bits of the address, and the values listed across the top of the chart. The one with two dots sets the 4 high bits. These are listed down the left of the chart.
If you need less than 16 elements from the memory bank, you only need one address input (typically the low bits) and can leave the other disconnected. That will give you 4 bit addressing, i.e. up to 16 locations.
Reading
The value stored in the memory bank is available through the top output and is present immediately if a clock is NOT used. As soon as the addresses change, the output will change to the new value.
The clock input is optional and works the same way as in SR latch. If it is connected, the address lines will only be read at the rising edge of the clock signal. At all other times the output of the memory bank will keep showing the last addressed location, no matter what is currently supplied to address lines. This is useful for synchronous or timed circuits.
Writing
In the rare case where you need to write to the memory block, you must use the data input (i.e. the one accessible when you place the memory bank on wire-through-block element). The value supplied on this input will be written at the address shown by address lines on the rising edge of the clock input, which must be 0.7V or less. Anything above 0.7V will cause a synchronous read, as described above. Since there IS a connection to the clock input, all reads must be 'synchronous'. Example circuits are presented below...
Editing
Memory block is manually editable. When you hold a memory block in your hand (or look at a mounted one from close distance), the sneak button will change into edit button, as seen in the picture below.
* * * WARNING * * *
Do NOT edit the bank when it's in-hand if you are in any survival mode. The game has a bug that will delete all banks in the selected slot EXCEPT ONE!. Once a bank is programmed, it becomes unique and cannot share an inventory slot with any other item. But you can hold a full stack of unprogrammed banks. If you then edit the stack as a whole, the game gets confused and will turn the entire stack into just one single (programmed) bank. Losing an entire stack of memories in cruel mode can be very frustrating!
* * * * *
Tap that button and an editing window will open up where you can enter the data. See the picture. Each entry in the middle is one memory location and is located by the numbers across the top and left side, much like a BINGO card. The numbers across the top represent the low 4 bits of the address (going into the single dot) and the ones down the left are the high 4 bits (the double dots).
The Memory Bank is Editable.
If you are only using one address signal and it's the low one, the only locations that matter are the first row across. If however, you have to use ONLY the high 4 bit signal, then you can only access the first COLUMN down the left.
To edit the memory, tap on the row you need to change and an entry dialog box will open showing the current contents of that row. Changing the contents from this point is device dependant and may not be the same for everyone. Sorry.
The 'Linear" button will let you fill in the entire 256 locations in one entry. This can be very error prone to enter by hand, but you can use this way to copy-paste the entire chart at once. Copy it from another app and you should be able to paste it into this box.
Applications
The value in memory banks will stay valid even when the Player moves very far away.
- The most obvious use is to store data for later access. Applications for this are many - one could be to have certain numbers show on a 7-segment display when certain switches are active.
- Useful in active or simulated displays.
- Can control 4 digital devices according to the input of up to 8 different signals.
- Can be a decoder - translate any analog value to any other value at random or by function.
Analog Latch
A latch is used to 'capture' a reading on the data input. This is used where a signal may be changing over time and you want to get the value at one specific time. There is an article dedication to using the memory bank as a latch or register.
Analog Comparator
A comparator is simply a 'gate' that outputs a digital 1 when both inputs are exactly the same. This is the same as an inverted XOR, for pure digital inputs.
The two analog signals are fed to the two address inputs. The clock is left open. The memory's data output is (usually) a digital signal. The memory must be programmed with the compare function. The basic compare has the memory programmed to output a digital 1 (hex 'F') only when the low address line is the same as the high address line. The memory image for this is:
|| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 || 8 | 9 | A | B | C | D | E | F || 0 || F | | | | | | | || | | | | | | | || 1 || | F | | | | | | || | | | | | | | || 2 || | | F | | | | | || | | | | | | | || 3 || | | | F | | | | || | | | | | | | || 4 || | | | | F | | | || | | | | | | | || 5 || | | | | | F | | || | | | | | | | || 6 || | | | | | | F | || | | | | | | | || 7 || | | | | | | | F || | | | | | | | || 8 || | | | | | | | || F | | | | | | | || 9 || | | | | | | | || | F | | | | | | || A || | | | | | | | || | | F | | | | | || B || | | | | | | | || | | | F | | | | || C || | | | | | | | || | | | | F | | | || D || | | | | | | | || | | | | | F | | || E || | | | | | | | || | | | | | | F | || F || | | | | | | | || | | | | | | | F ||
All locations that are blank are actually filled with '0's. They are left out here for clarity. You can see that where the low address value (top) is the same as the high address value (left), the output will be 'F', or a digital 1. Wherever they are NOT the same, a zero is output.
You can copy the number below and paste it, if you like.
F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F0000000000000000F
This same circuit can be used for other compare functions, such as "less than" or "greater or equal" by simply changing the memory's 'matrix'. With more complicated programming, you could even have a "close-to" function output. This could be something like, "the output is 'F' when the inputs are exactly the same and it is '8' if the difference is 1 or '4' if the difference is 2 or '0' if it's more". That's just one example of a more complicated compare function and is usually called 'fuzzy' math.
PLD
Any memory bank can be used as a general purpose "Programmable Logic Device". This means that it can be used to replace a huge amount of individual logic gates. Each and every possible combination of all 8 address lines (the 2 address inputs) can be programmed to output any pattern on the 4 output bits. Programming the memory for a general use PLD can be very tricky. Engineers using even small PLDs usually have a special program to determine the matrix values from their function's equations. Each application of course, is unique so examples are not offered.
Addition Module
One specific application of the PLD is as an addition module. One memory bank can be programmed to do (unsigned) addition on two inputs. Each input can only be 3 bits wide, however. Two 3 bit values can add up to a 4 bit result. Since there are only 4 output bits, three bit values are the most that can be added. The 4th output bit can be used as a carry into a higher stage addition module, to let you add larger numbers. Addition modules are 'chained' that way. The data matrix for a basic adder is below:
|| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 || 8 | 9 | A | B | C | D | E | F || 0 || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 || | | | | | | | || 1 || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 || | | | | | | | || 2 || 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 || | | | | | | | || 3 || 3 | 4 | 5 | 6 | 7 | 8 | 9 | A || | | | | | | | || 4 || 4 | 5 | 6 | 7 | 8 | 9 | A | B || | | | | | | | || 5 || 5 | 6 | 7 | 8 | 9 | A | B | C || | | | | | | | || 6 || 6 | 7 | 8 | 9 | A | B | C | D || | | | | | | | || 7 || 7 | 8 | 9 | A | B | C | D | E || | | | | | | | || 8 || | | | | | | | || | | | | | | | || 9 || | | | | | | | || | | | | | | | || A || | | | | | | | || | | | | | | | || B || | | | | | | | || | | | | | | | || C || | | | | | | | || | | | | | | | || D || | | | | | | | || | | | | | | | || E || | | | | | | | || | | | | | | | || F || | | | | | | | || | | | | | | | ||
Only 1/4 of the array is used because we are not using the highest bit of the inputs and the rest of the values can all be left at '0'. To see how the added works, let's find for instance, 5 + 4. First find 5 at the top and 4 on the left. Where they cross is the output value, of 9.
In order to 'chain' the addition blocks, a 'carry in' bit must be used. It has to be one of the inputs' 4th bits but it can be on either input if the memory is programmed for it. Remember that any input not connected is assumed to be '0'.
If the carry is '1'. it means we have to add a 1 to the result. A carry can only be a 1 in computer numbers (binary). So we take the quarter we already have, add one to each location and paste it where either 4th bit is a '1'.
This chart looks like this:
|| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 || 8 | 9 | A | B | C | D | E | F || 0 || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 || 1 || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 || 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 || 2 || 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 || 3 | 4 | 5 | 6 | 7 | 8 | 9 | A || 3 || 3 | 4 | 5 | 6 | 7 | 8 | 9 | A || 4 | 5 | 6 | 7 | 8 | 9 | A | B || 4 || 4 | 5 | 6 | 7 | 8 | 9 | A | B || 5 | 6 | 7 | 8 | 9 | A | B | C || 5 || 5 | 6 | 7 | 8 | 9 | A | B | C || 6 | 7 | 8 | 9 | A | B | C | D || 6 || 6 | 7 | 8 | 9 | A | B | C | D || 7 | 8 | 9 | A | B | C | D | E || 7 || 7 | 8 | 9 | A | B | C | D | E || 8 | 9 | A | B | C | D | E | F || 8 || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 || | | | | | | | || 9 || 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 || | | | | | | | || A || 3 | 4 | 5 | 6 | 7 | 8 | 9 | A || | | | | | | | || B || 4 | 5 | 6 | 7 | 8 | 9 | A | B || | | | | | | | || C || 5 | 6 | 7 | 8 | 9 | A | B | C || | | | | | | | || D || 6 | 7 | 8 | 9 | A | B | C | D || | | | | | | | || E || 7 | 8 | 9 | A | B | C | D | E || | | | | | | | || F || 8 | 9 | A | B | C | D | E | F || | | | | | | | ||
Here's the linear stream for it:
01234567123456781234567823456789234567893456789A3456789A456789AB456789AB56789ABC56789ABC6789ABCD6789ABCD789ABCDE789ABCDE89ABCDEF123456780000000023456789000000003456789A00000000456789AB0000000056789ABC000000006789ABCD00000000789ABCDE0000000089ABCDEF00000000
Remember that the number input can only be from 0 through 7 and repeats under the carry portion. Where the matrix has a 'D' input for example, the number input is actually a '5' but the carry is also a +1. If take the previous example of 5 + 4 and assume the carry is +1, we will go to the 'D' at the top (which is 5 +carry) and follow it down until it crosses the '4' row. (Carry only applies to one input.) The answer is 'A', or 10. (5 + 4) + 1 = 10
The biggest difficulty we have to build this, is separating out the bits from the 'analog' signals. Analog signals naturally contain 4 bits of data. We can only add 3 at a time with this module. If we're adding more than three bits, that means we have to split out the bits in the analog signal and rearrange them to fit the adder. That also means that the adders HAVE to be chained and that means the 4th output bit is actually a carry-out. This bit also has to be split out from the analog output signal.
To split the bits out, we use an A>D to separate the bits, rearrange them and use a D>A to recombine them into an analog signal. This has to be done to each address input as well as the data output.
Addition of other 'types' of numbers, such as signed integers, BCD, exponentials, etc. gets very complex and should never be needed in any SC setting.
Clock Input Use
This section presents circuits to control the clock input when you wish to write electrically to the memory.
If you need to write to the memory but do not need synchronous reads, the circuit is quite simple. You will have a digital control signal that tells when to write to the memory. This signal needs to be 0 to write and 1 to read. If it's the other way, just add a NOT in series. You will also need a fixed voltage reference that is 0.1V to 0.7V. One easy way to do this is to use a battery and program it to 0.7V. Then you just feed this into one side of an OR gate and the write control into the other input. Then feed the OR gate output into the memory clock input. This makes the clock input value either 'F' (to read) or '7' (to write).
The basic logic gates pass through an analog signal. This (technical) page explains it but you don't need to know that in order to make it. It basically means that when the button is pressed (goes to 1), the battery voltage will be sent to the memory clock input. When the button is off or 0, the clock input is 1.
See the picture:
This circuit gets more complicated if you need to write yet still have regular, clocked synchronous operation. The write voltage must be disabled separately from the clock input and this really just requires an additional AND gate.
WRITE ENABLE lets the write (low) voltage pass through to the memory.
SYSTEM CLOCK is normally the memory read signal. The memory reads from the address when this goes high.
For a write to the memory, the WRITE ENABLE must be 1 while the clock is low. The write address must be ready before the OR's output goes (low) to the write voltage. This circuit can be used if you want to program a memory in adventure mode or from a distance (a control panel?).
Further Information
More information on creating the clock input signal can be found on this page. It provides simpler ways to convert the voltages.