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Difference between revisions of "v0.34:Minecart logic"

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The addition of [[minecart]]s to Dwarf Fortress has opened up new and exciting logic and computing options for the ambitious fortress manager. Minecart-based logic gates and memory cells are easy to build (arguably easier than [[fluid logic]] systems), they are easy to reconfigure, and react quickly.
+
The addition of [[minecart]]s to Dwarf Fortress has opened up new and exciting logic and computing options for the ambitious fortress manager. Minecart-based logic gates and memory cells are easy to build, quick to react, and can even be built without power, water, or creatures.  The training your [[doctor]]s will receive is just one of many reasons to compute with minecarts!
  
 
==Techniques and Circuits==
 
==Techniques and Circuits==
Line 10: Line 10:
  
 
====Key====
 
====Key====
−
Adequately diagramming minecart logic devices can be difficult; each tile on each z-level might need to display up to four slices (track, ramp, furniture, minecart) that can lay on top of each other.  Ramps are displayed on the furniture layer for the sake of simplicity, and some slices may be omitted when unnecessary.  Components of each lower slice are displayed on the higher slice when unchanged by new components to give the reader a sense of placement.  Wall {{Raw Tile|O|#FFF|#000}} is typically displayed only where it is essential to the operation of the circuit.  Unengraved floor {{Raw Tile|,|#FFF|#000}} is sometimes needed for other components, but of course can be smoothed as desired.  Track direction is laid out with {{Raw Tile|║|#FFF|#000}}{{Raw Tile|═|#FFF|#000}}{{Raw Tile|╗|#FFF|#000}}{{Raw Tile|╝|#FFF|#000}}{{Raw Tile|╚|#FFF|#000}}{{Raw Tile|╔|#FFF|#000}} and ends in a tile with {{Raw Tile|╨|#FFF|#000}}{{Raw Tile|╥|#FFF|#000}}{{Raw Tile|╡|#FFF|#000}}{{Raw Tile|╞|#FFF|#000}}.  Minecarts {{Raw Tile|■|#FFF|#000}} are accelerated by rollers to the east {{Raw Tile|╟|#FFF|#000}} west {{Raw Tile|╢|#FFF|#000}} north {{Raw Tile|╧|#FFF|#000}} or south {{Raw Tile|╤|#FFF|#000}} and decelerated by track stops {{Raw Tile|≡|#FFF|#000}}.  Rollers are controlled via gear assemblies, either engaged {{Raw Tile|☼|#FFF|#000}} or disengaged {{Raw Tile|☼|#777|#000}}, typically connected to sufficient power {{Raw Tile|P|#0F0|#000}}.  Pressure plates {{Raw Tile|^|#FFF|#000}} provide output and, in some cases, modulate the circuit itself; in such cases, they are typically colored to make it clear to which components they are linked.  Up {{Raw Tile|▲|#FFF|#000}} and down {{Raw Tile|▼|#FFF|#000}} ramps may be necessary to travel z-levels or alter minecart velocity; they may be roofed or covered with empty space {{Raw Tile|.|#0FF|#000}} in some views.  Doors {{Raw Tile|┼|#FFF|#000}}, hatches {{Raw Tile|¢|#FFF|#000}}, and retractable bridges {{Raw Tile|╬|#000|#CCC}} are commonly used to control the path of minecarts.  Where necessary, clarification can be found in the descriptions of each circuit.
+
Adequately diagramming minecart logic devices can be difficult; each tile on each z-level might need to display up to four slices (track, [[ramp]], [[furniture]], minecart) that can lay on top of each other.  Ramps are displayed on the furniture layer for the sake of simplicity, and some slices may be omitted when unnecessary.  Components of each lower slice are displayed on the higher slice when unchanged by new components to give the reader a sense of position.  Wall {{Raw Tile|O|#FFF|#000}} is typically displayed only where it is essential to the operation of the circuit, and drawn only as sequences of pillars to avoid confusion with track.  Unengraved floor {{Raw Tile|,|#FFF|#000}} is sometimes needed for other components, but of course can be smoothed as desired.  Track direction is laid out with {{Raw Tile|║|#FFF|#000}}{{Raw Tile|═|#FFF|#000}}{{Raw Tile|╗|#FFF|#000}}{{Raw Tile|╝|#FFF|#000}}{{Raw Tile|╚|#FFF|#000}}{{Raw Tile|╔|#FFF|#000}}{{Raw Tile|╩|#FFF|#000}} and ends in a tile with {{Raw Tile|╨|#FFF|#000}}{{Raw Tile|╥|#FFF|#000}}{{Raw Tile|╡|#FFF|#000}}{{Raw Tile|╞|#FFF|#000}}.  Minecarts {{Raw Tile|■|#FFF|#000}} are accelerated by rollers to the east {{Raw Tile|╟|#FFF|#000}} west {{Raw Tile|╢|#FFF|#000}} north {{Raw Tile|╧|#FFF|#000}} or south {{Raw Tile|╤|#FFF|#000}} and decelerated by track stops {{Raw Tile|≡|#FFF|#000}}.  Rollers are controlled via [[Gear_assembly|gear assemblies]], either engaged {{Raw Tile|☼|#FFF|#000}} or disengaged {{Raw Tile|☼|#777|#000}}, typically connected to sufficient [[power]] {{Raw Tile|P|#0F0|#000}}.  [[Pressure plate]]s {{Raw Tile|^|#FFF|#000}} provide output and, in some cases, modulate the circuit itself.  Up {{Raw Tile|▲|#FFF|#000}} and down {{Raw Tile|▼|#FFF|#000}} ramps may be necessary to travel z-levels or alter minecart velocity; they may be roofed or covered with empty space {{Raw Tile|.|#0FF|#000}} in some views.  [[Hatch]]es {{Raw Tile|¢|#FFF|#000}} and retractable [[bridge]]s {{Raw Tile|╬|#000|#CCC}} are commonly used to control the path of minecarts.  Where necessary, clarification can be found in the descriptions of each circuit.
  
 
===Power to signal===
 
===Power to signal===
Line 22: Line 22:
  
  
−
In this simplest of all designs, the output plate sends an '''on''' signal when the gear assemblies {{Raw Tile|☼|#FFF|#000}} are powered {{Raw Tile|P|#0F0|#000}}.  When power is lost, the minecart settles onto either the northern or southern roller spaces, and the output plate sends an '''off''' signal.
+
In this, the simplest of all designs, the output plate sends an '''on''' signal when the gear assemblies {{Raw Tile|☼|#FFF|#000}} are powered {{Raw Tile|P|#0F0|#000}}.  When power is lost, the minecart settles onto either the northern or southern roller spaces, and the output plate sends an '''off''' signal.
 
   
 
   
−
This device is very general purpose.  Left as an exercise for the reader, alternate construction can result in a [[repeater]] or edge detection.
+
This device is very general purpose.  Left as an exercise for the reader, alternate construction can result in edge detection or in a [[repeater]] design.
  
 
===Newton's Cradle Memory===
 
===Newton's Cradle Memory===
 
{{diagram|spaces=yes|\
 
{{diagram|spaces=yes|\
 
   O      O        O
 
   O      O        O
−
   ╥,      ╤[#0C0]☼[#0F0]P      ╤[#0C0]☼[#0F0]P
+
   ╥,      ╤[#0C0]☼[#0F0]P      [#000][#0f0]■[#0C0]☼[#0F0]P
−
   ║      ║        [#000][#0f0]■
+
   ║      ║        ║
−
   ║      [#F0F]^        [#F0F]^
+
   ║      [#F0F]^        [#000][#ff0]■
−
   ╨,      ╧[#0CC]☼[#0F0]P      [#000][#0ff]■[#0CC]☼[#0F0]P
+
   ╨,      ╧[#CC0]☼[#0F0]P      ╧[#CC0]☼[#0F0]P
 
   O      O        O
 
   O      O        O
 
track furniture minecart}}
 
track furniture minecart}}
  
  
−
TinyPirate's Newton's Cradle [[Memory_(computing)|memory]] cell is notable both for it's tiny footprint and for demonstrating an important principle of minecarts.  When the southern gear assembly {{Raw Tile|☼|#0CC|#000}} is briefly engaged, the southern roller {{Raw Tile|╧|#FFF|#000}} becomes powered, launching the southern minecart {{Raw Tile|■|#0FF|#000}} onto the output plate {{Raw Tile|^|#F0F|#000}}. But rather than continuing past the output plate, the southern minecart collides with the northern minecart {{Raw Tile|■|#0F0|#000}}, sending it onto the northern (unpowered) roller.  When the northern gear assembly is briefly engaged, the situation reverses: the northern minecart knocks the southern minecart off of the output plate.
+
[[User:TinyPirate|TinyPirate]]'s Newton's Cradle [[Memory_(computing)|memory]] cell is notable both for its small footprint and for demonstrating an important principle of minecarts.  When the northern gear assembly {{Raw Tile|☼|#0C0|#000}} is briefly engaged, the northern roller {{Raw Tile|╤|#FFF|#000}} becomes powered, launching the northern minecart {{Raw Tile|■|#000|#0F0}} into the southern minecart {{Raw Tile|■|#000|#FF0}}. The southern minecart then leaves the output plate {{Raw Tile|^|#F0F|#000}} and settles on the southern (unpowered) roller.  When the southern gear assembly is briefly engaged, the situation reverses: the southern minecart settles on the output plate, knocking the northern minecart onto the northern (unpowered) roller-- as in its original state.
  
−
===Roller derailer OR===
+
===Continuous roller OR===
 +
{{diagram|spaces=yes|\
 +
╔═╗═╗  ╔═╗═╗
 +
║ ║O║  ║ [#F0F]^O║
 +
║ ║O║  ╤[#0F0]☼╧O║
 +
║ ║O║  [#0F0]P╤[#FF0]☼╧O║
 +
╚═╩═╝  ╚═╧═╝
 +
track  furniture}}
 +
[http://www.bay12forums.com/smf/index.php?topic=114923.msg3891809#msg3891809 Veylon's] roller OR continuously evaluates two operands via a minecart traveling counter-clockwise using principles of power transmission through single tile rollers.  Should either input {{Raw Tile|☼|#0F0|#000}} or {{Raw Tile|☼|#FF0|#000}} be engaged, power {{Raw Tile|P|#0F0|#000}} is transmitted to the southernmost, S->N roller {{Raw Tile|╧|#FFF|#000}}.  Although the minecart is left with diagonal velocity, walls prevent derailment.  When neither input is engaged, the minecart continues over the T-junction to the east, missing the output plate {{Raw Tile|^|#F0F|#000}}.
 +
 
 +
===Roller switched AND===
 
{{diagram|spaces=yes|\
 
{{diagram|spaces=yes|\
 
   ║      ║
 
   ║      ║
−
   ║╗O    [#0F0]P[#0F0]╟╗O
+
   ╔╗    [#0F0]P[#0F0]╧╗
−
   ║║O    ║║O
+
   ║║      ║║
−
   ║╗O    [#0F0]P[#0FF]╟║O
+
   ╔╗    [#0F0]P[#FF0]╧╗
−
   ║║O    [#F0F]^║O
+
   ║║      [#F0F]^║
 
   ╚╗      ╚╗
 
   ╚╗      ╚╗
 
track  furniture}}
 
track  furniture}}
−
In this gate, a minecart entering from the south is diverted by W->E rollers {{Raw Tile|╟|#0F0|#000}} and {{Raw Tile|╟|#0FF|#000}} onto an alternate pathway whenever either is active (that is, when neither has received an '''on''' signal).  A slight redesign could easily evaluate OR by power rather than signal; another slight change would make this a NOR gate instead.
+
[[User:Larix|Larix]]'s roller-switched AND takes advantage of the behavior of rollers to avoid troublesome diagonal velocity.  It is potentially confusing both for the counter-intuitive direction of its rollers as well as the way that rollers respond to signals.  When the minecart encounters either activated (that is, the last signal received was an '''off''') S->N roller {{Raw Tile|╧|#FF0|#000}} or {{Raw Tile|╧|#0F0|#000}}, its velocity is completely rewritten and reversed, sending it onto the alternate (clockwise) path.  Should neither roller be activated (that is, the last signal received by both was an '''on'''), the track bends will be ignored and the minecart will travel directly south, over the output plate {{Raw Tile|^|#F0F|#000}}.
  
−
===Bridge drop/bridge derailer AND===
+
===Resetting bridge-derailment AND===
 
{{diagram|spaces=yes|\
 
{{diagram|spaces=yes|\
−
  ║    ║      ║
+
O[#0FF].═[#0FF]. O▼═▼  O[#FF0]¢═▼
−
  [#0FF].   ▼      [#000][#0f0]╬
+
     
−
  ║    ║      ║
+
     
−
  ║    ║      ║
+
     
−
  [#0FF].    ▼      ▼
 
−
  O    O      O
 
 
track ramp furniture
 
track ramp furniture
−
      Z+1
+
z+1
−
   O    O      O
+
O╔O╗ O▲O▲   O▲O▲
−
   ║    ▲      ▲
+
   ╚═╚  ╚═▲   [#000][#0f0]╬[#F0F]^▲
−
  ╚╗   ╚╗    [#000][#0ff]╬╗
+
   ╚═╝  ╚═╝   ╚═╝
−
O╗║  O▲║    O▲[#F0F]^
 
−
   ╔╝   ╔╝    ╔╝
 
 
track ramp furniture
 
track ramp furniture
−
      Z+0}}
+
z+0}}
 +
 
 +
When both the yellow hatch {{Raw Tile|¢|#FF0|#000}} and the green retractable bridge {{Raw Tile|╬|#000|#0F0}} are open, minecarts on this circuit make a continuous loop, triggering the output plate {{Raw Tile|^|#F0F|#000}}.  If either is closed, the plate is never activated.  If the bridge is closed, the minecart derails to the southern path, avoiding the plate.  If the hatch is closed, the minecart is unable to drop into the northwest ramp, and so sits on the upper, northwestern tile until the hatch opens.
 +
 
 +
There are many concerns when using a gate like this.  Minecarts can be flung when a bridge changes state underneath them, and unfortunately, hatch covers cannot provide the same derailment effect on flat track.  Additionally, because your minecart never evaluates both operands at exactly the same moment, it's possible for this gate to output when neither operand is actually true (i.e., last received an '''on''' signal) at the same moment.
 +
 
 +
It's not always a problem, but this behavior is common to AND gates.  Paradoxically, one solution is to moderate your inputs via an extra AND gate; this design shows how that can be done.  When a large number of circuits such as that shown are created and the hatches of all of them are linked to a single lever, a quick flick (on and off) of that lever can guarantee that all of your circuits fire at the same time-- that is, that all of your inputs for the next computation change state simultaneously.  The minecarts then return to their position atop the hatches, ready for another flick of your clock lever.
 +
 
 +
Worth noting, as well, is the central eastern impulse ramp that allows the minecart to maintain enough velocity to complete this circuit.  Impulse ramps like this can be used to make unpowered gates.  However, their behavior is unintuitive, and they should only be used with extreme caution.  For example, in the diagram above, such a device used for continuous AND evaluation (rather than the resetting AND suggested in the text) is likely to accelerate the minecart on each pass, such that the minecart will stop moving after some number of circuits.
 +
 
 +
===MPL NOT===
 +
{{diagram|spaces=yes|\
 +
 +
O,      O,
 +
track    ramp
 +
z+2
 +
  ╔═╗      ╔═╗      ╔═╗
 +
O══[#0FF].[#0FF].╝  O▲═▼▼╝  O▲[#F0F]^▼[#0F0]¢╝
 +
track    ramp  furniture
 +
z+1
 +
 +
OOO══O  OOO▲▲O
 +
track    ramp
 +
z+0
 +
}}
  
−
While impractical, this AND gate demonstrates a few useful principles.  If the green retractable bridge {{Raw Tile|╬|#000|#0F0}} is closed, a minecart entering from the north travels over it, eventually dropping one z-level at the southernmost ramp before continuing southward.  If that bridge is open but the cyan retractable bridge {{Raw Tile|╬|#000|#0FF}} is closed, the minecart drops into the northern ramp and continues straight south, since the bridge covers the track.  Only should both bridges be open will the minecart drop, then divert onto the eastern path, triggering its output plate {{Raw Tile|^|#F0F|#000}}.
+
Larix's [[User:Larix/MPL/2|powerless logic gates]] avoid the reliability and latency issues that plague many minecart designs through the use of paired impulse ramps and hatches that control not just path, but direction of movement.  A minecart traveling the pictured circuit while the input hatch {{Raw Tile|¢|#0F0|#000}} is open will settle into a counter-clockwise path, regardless of the direction of its initial velocity.  Yet when the hatch becomes closed, the minecart cannot travel counter-clockwise, but instead is accelerated in the clockwise direction, onto the output plate {{Raw Tile|^|#F0F|#000}}.  It will then oscillate between the far east and far west ramps until the hatch is opened, at which point it will resume counter-clockwise motion.
  
−
Note that using bridges in this manner can be very tricky.  When bridges change state, minecarts traveling over them are liable to be thrown.  Bridges can still be useful in some circuits where the player is certain of the timing involved.  For instance, in this circuit, if the player knows that the green bridge and the cyan bridge will only ever change state at the same time, and the minecart travelling the circuit rests atop the green bridge rather than entering the circuit at unpredictable times, the above circuit is safe.
+
Use of ramps with high-velocity minecarts may necessitate ceilings as demonstrated on z+2.  The exact nature of the ceiling (floor, wall) is unimportant.  Some diagrammed walls are unnecessary for the design and are drawn to help the reader in orientation.
  
−
Also note that should the cyan input change very soon after the green input, there is the potential for this circuit to output when the inputs are not actually true at the same exact instant.  This problem is common in AND gates.  Should this be important to your design, it is possible to work around it, paradoxically, with another AND gate, by ANDing your inputs with a regularly pulsed [[Repeater|clock]] signal.  The bridge-drop (or its superior variant, the hatch-drop), linked to a clock, can be used to create circuits where all of your inputs change state at the same time.
+
===Other techniques and gates===
 +
Any logic gate can be made with a combination of those shown.  NAND, for instance, is NOT AND; XOR is OR AND (NOT AND).  Clocks and edge detection are suggested and proven designs exist, if not on this page.  But the examples above were chosen for the disparate techniques they demonstrate.  The interested reader is encouraged to further research, or the design of his or her own gates.
  
−
== Potential as an independent logic discipline ==
+
Doors can be used to block the travel of a minecart through a circuit, or to prevent derailment, although for reliability's sake, care needs to be taken that the door cannot change state while the minecart is in motion, or it may jam on top of the minecart.  [[Floodgate]]s won't jam in this fashion, although they do introduce some latency.  Minecarts of multiple weights, with pressure plates that trigger only on the weight of one, may be used in certain designs; Bloodbeard's fantastically tiny [http://www.bay12forums.com/smf/index.php?topic=114923.msg3532411#msg3532411 load-adjusted memory cell] is a good example.  Rollers can be used perpendicularly to a track to derail a cart and impart diagonal velocity.  Switchable track stops can prevent or permit derailment.  The possibilities are far from exhausted-- and that's assuming one is only interested in ''practical'' techniques.
  
−
Minecarts can also be set in motion by ramps and switched between different paths by buildings, opening the path for a powerless logic discipline. The basic binary logic gates can be built in this fashion and combined to perform other operations like counting or basic algebra. The circuits tend to look quite complicated, especially if they stretch over multiple levels.
+
==Integration with other disciplines==
 +
There's no reason minecart logic needs to be used in isolation. Combining it with other logical disciplines allows one to use each where it is strong, and avoid each where it is weak.
  
−
[[File:Äquivalenz-Differenz.png]]
+
===[[Mechanical logic]]===
 +
This is the most obvious choice.  Mechanical logic offers the potential for incredible speed, yet requires a medium to generate useful signals or to create delay (hence, to create repeaters), and it's hard to use gear assemblies as memory cells.  Minecart logic excels at precisely these tasks.  Minecart-based power-to-signal and memory are tiny and fast.  Minecart-based delay is precisely tunable.  The superiority of minecart logic has made water obsolete for these purposes.
  
−
This kind of minecart logic is primarily an alternative to [[creature logic]]. Since minecarts move relatively quickly and completely deterministically, simple minecart logic gates can be relatively small and quick. Since a minecart only reacts to the conditions of its current tile and the tile it tries to move into, creature logic will have an advantage when looking at multiple and long logic paths, where a creature instantly detects and chooses the open path, while the minecart has to check every tile and building separately.  
+
===[[Creature logic]]===
 +
Minecart logic, particularly Larix's powerless MPL logic, has replaced creature logic as the logic-of-last-resort (for when power and fluid are unavailable) or first-resort (for when computation is desired before power can be set up or fluid accessed).  However, for the borg logic hobbyist, integration with minecarts suggests interesting possibilities.  It is difficult to imagine a simpler clock than a minecart with a "push always after x days" condition, and guided minecarts offer unprecedented control over the path of [[dwarf|dwarves]].
  
−
For signal generation, memory cells, repeaters and adders, this kind of minecart logic offers a variety of options.
+
===[[Fluid logic]]===
 +
Minecart logic outperforms fluid logic sufficiently to have mostly replaced it.  However, the problem of automated fluid delivery may be best solved through some fluid logic techniques, and may suggest some [[stupid dwarf trick]]s for those that want to use the fluid capacity of minecarts to compute.
  
 
== See Also ==
 
== See Also ==

Latest revision as of 22:55, 8 April 2014

xTATTEREDx  · +FINE+  · *SUPERIOR*  · ≡EXCEPTIONAL≡  · ☼MASTERWORK☼
Part of a series on
Computing
7x191.PNG
Logic: Animal • Creature • Fluid • Mechanical • Minecart
Components: Adder • Memory • Repeater
v · t · e
v50.14 · v0.47 · v0.34.11 · v0.31 · v0.28 · v0.23
This article is about an older version of DF.

The addition of minecarts to Dwarf Fortress has opened up new and exciting logic and computing options for the ambitious fortress manager. Minecart-based logic gates and memory cells are easy to build, quick to react, and can even be built without power, water, or creatures. The training your doctors will receive is just one of many reasons to compute with minecarts!

Techniques and Circuits[edit]

There exist a great number of different techniques by which a minecart can receive input, compute, and deliver output. This article does not aim for a comprehensive list of techniques and circuits; the interested reader is encouraged to investigate further. The following examples were chosen to demonstrate both a variety of techniques and a few commonly used gates.

Key[edit]

Adequately diagramming minecart logic devices can be difficult; each tile on each z-level might need to display up to four slices (track, ramp, furniture, minecart) that can lay on top of each other. Ramps are displayed on the furniture layer for the sake of simplicity, and some slices may be omitted when unnecessary. Components of each lower slice are displayed on the higher slice when unchanged by new components to give the reader a sense of position. Wall O is typically displayed only where it is essential to the operation of the circuit, and drawn only as sequences of pillars to avoid confusion with track. Unengraved floor , is sometimes needed for other components, but of course can be smoothed as desired. Track direction is laid out with ║═╗╝╚╔╩ and ends in a tile with ╨╥╡╞. Minecarts ■ are accelerated by rollers to the east ╟ west ╢ north ╧ or south ╤ and decelerated by track stops ≡. Rollers are controlled via gear assemblies, either engaged ☼ or disengaged ☼, typically connected to sufficient power P. Pressure plates ^ provide output and, in some cases, modulate the circuit itself. Up ▲ and down ▼ ramps may be necessary to travel z-levels or alter minecart velocity; they may be roofed or covered with empty space . in some views. Hatches ¢ and retractable bridges ╬ are commonly used to control the path of minecarts. Where necessary, clarification can be found in the descriptions of each circuit.

Power to signal[edit]

O O
╥ , ╤ ☼
║ ^ P
╨ , ╧ ☼
O O
t r a c k f u r n i t u r e


In this, the simplest of all designs, the output plate sends an on signal when the gear assemblies ☼ are powered P. When power is lost, the minecart settles onto either the northern or southern roller spaces, and the output plate sends an off signal.

This device is very general purpose. Left as an exercise for the reader, alternate construction can result in edge detection or in a repeater design.

Newton's Cradle Memory[edit]

O O O
╥ , ╤ ☼ P ■ ☼ P
║ ║ ║
║ ^ ■
╨ , ╧ ☼ P ╧ ☼ P
O O O
t r a c k f u r n i t u r e m i n e c a r t


TinyPirate's Newton's Cradle memory cell is notable both for its small footprint and for demonstrating an important principle of minecarts. When the northern gear assembly ☼ is briefly engaged, the northern roller ╤ becomes powered, launching the northern minecart ■ into the southern minecart ■. The southern minecart then leaves the output plate ^ and settles on the southern (unpowered) roller. When the southern gear assembly is briefly engaged, the situation reverses: the southern minecart settles on the output plate, knocking the northern minecart onto the northern (unpowered) roller-- as in its original state.

Continuous roller OR[edit]

╔ ═ ╗ ═ ╗ ╔ ═ ╗ ═ ╗
║ ║ O ║ ║ ^ O ║
║ ║ O ║ ╤ ☼ ╧ O ║
║ ║ O ║ P ╤ ☼ ╧ O ║
╚ ═ ╩ ═ ╝ ╚ ═ ╧ ═ ╝
t r a c k f u r n i t u r e

Veylon's roller OR continuously evaluates two operands via a minecart traveling counter-clockwise using principles of power transmission through single tile rollers. Should either input ☼ or ☼ be engaged, power P is transmitted to the southernmost, S->N roller ╧. Although the minecart is left with diagonal velocity, walls prevent derailment. When neither input is engaged, the minecart continues over the T-junction to the east, missing the output plate ^.

Roller switched AND[edit]

║ ║
╔ ╗ P ╧ ╗
║ ║ ║ ║
╔ ╗ P ╧ ╗
║ ║ ^ ║
╚ ╗ ╚ ╗
t r a c k f u r n i t u r e

Larix's roller-switched AND takes advantage of the behavior of rollers to avoid troublesome diagonal velocity. It is potentially confusing both for the counter-intuitive direction of its rollers as well as the way that rollers respond to signals. When the minecart encounters either activated (that is, the last signal received was an off) S->N roller ╧ or ╧, its velocity is completely rewritten and reversed, sending it onto the alternate (clockwise) path. Should neither roller be activated (that is, the last signal received by both was an on), the track bends will be ignored and the minecart will travel directly south, over the output plate ^.

Resetting bridge-derailment AND[edit]

O . ═ . O ▼ ═ ▼ O ¢ ═ ▼
t r a c k r a m p f u r n i t u r e
z + 1
O ╔ O ╗ O ▲ O ▲ O ▲ O ▲
╚ ═ ╚ ╚ ═ ▲ ╬ ^ ▲
╚ ═ ╝ ╚ ═ ╝ ╚ ═ ╝
t r a c k r a m p f u r n i t u r e
z + 0

When both the yellow hatch ¢ and the green retractable bridge ╬ are open, minecarts on this circuit make a continuous loop, triggering the output plate ^. If either is closed, the plate is never activated. If the bridge is closed, the minecart derails to the southern path, avoiding the plate. If the hatch is closed, the minecart is unable to drop into the northwest ramp, and so sits on the upper, northwestern tile until the hatch opens.

There are many concerns when using a gate like this. Minecarts can be flung when a bridge changes state underneath them, and unfortunately, hatch covers cannot provide the same derailment effect on flat track. Additionally, because your minecart never evaluates both operands at exactly the same moment, it's possible for this gate to output when neither operand is actually true (i.e., last received an on signal) at the same moment.

It's not always a problem, but this behavior is common to AND gates. Paradoxically, one solution is to moderate your inputs via an extra AND gate; this design shows how that can be done. When a large number of circuits such as that shown are created and the hatches of all of them are linked to a single lever, a quick flick (on and off) of that lever can guarantee that all of your circuits fire at the same time-- that is, that all of your inputs for the next computation change state simultaneously. The minecarts then return to their position atop the hatches, ready for another flick of your clock lever.

Worth noting, as well, is the central eastern impulse ramp that allows the minecart to maintain enough velocity to complete this circuit. Impulse ramps like this can be used to make unpowered gates. However, their behavior is unintuitive, and they should only be used with extreme caution. For example, in the diagram above, such a device used for continuous AND evaluation (rather than the resetting AND suggested in the text) is likely to accelerate the minecart on each pass, such that the minecart will stop moving after some number of circuits.

MPL NOT[edit]

O , O ,
t r a c k r a m p
z + 2
╔ ═ ╗ ╔ ═ ╗ ╔ ═ ╗
O ═ ═ . . ╝ O ▲ ═ ▼ ▼ ╝ O ▲ ^ ▼ ¢ ╝
t r a c k r a m p f u r n i t u r e
z + 1
O O O ═ ═ O O O O ▲ ▲ O
t r a c k r a m p
z + 0

Larix's powerless logic gates avoid the reliability and latency issues that plague many minecart designs through the use of paired impulse ramps and hatches that control not just path, but direction of movement. A minecart traveling the pictured circuit while the input hatch ¢ is open will settle into a counter-clockwise path, regardless of the direction of its initial velocity. Yet when the hatch becomes closed, the minecart cannot travel counter-clockwise, but instead is accelerated in the clockwise direction, onto the output plate ^. It will then oscillate between the far east and far west ramps until the hatch is opened, at which point it will resume counter-clockwise motion.

Use of ramps with high-velocity minecarts may necessitate ceilings as demonstrated on z+2. The exact nature of the ceiling (floor, wall) is unimportant. Some diagrammed walls are unnecessary for the design and are drawn to help the reader in orientation.

Other techniques and gates[edit]

Any logic gate can be made with a combination of those shown. NAND, for instance, is NOT AND; XOR is OR AND (NOT AND). Clocks and edge detection are suggested and proven designs exist, if not on this page. But the examples above were chosen for the disparate techniques they demonstrate. The interested reader is encouraged to further research, or the design of his or her own gates.

Doors can be used to block the travel of a minecart through a circuit, or to prevent derailment, although for reliability's sake, care needs to be taken that the door cannot change state while the minecart is in motion, or it may jam on top of the minecart. Floodgates won't jam in this fashion, although they do introduce some latency. Minecarts of multiple weights, with pressure plates that trigger only on the weight of one, may be used in certain designs; Bloodbeard's fantastically tiny load-adjusted memory cell is a good example. Rollers can be used perpendicularly to a track to derail a cart and impart diagonal velocity. Switchable track stops can prevent or permit derailment. The possibilities are far from exhausted-- and that's assuming one is only interested in practical techniques.

Integration with other disciplines[edit]

There's no reason minecart logic needs to be used in isolation. Combining it with other logical disciplines allows one to use each where it is strong, and avoid each where it is weak.

Mechanical logic[edit]

This is the most obvious choice. Mechanical logic offers the potential for incredible speed, yet requires a medium to generate useful signals or to create delay (hence, to create repeaters), and it's hard to use gear assemblies as memory cells. Minecart logic excels at precisely these tasks. Minecart-based power-to-signal and memory are tiny and fast. Minecart-based delay is precisely tunable. The superiority of minecart logic has made water obsolete for these purposes.

Creature logic[edit]

Minecart logic, particularly Larix's powerless MPL logic, has replaced creature logic as the logic-of-last-resort (for when power and fluid are unavailable) or first-resort (for when computation is desired before power can be set up or fluid accessed). However, for the borg logic hobbyist, integration with minecarts suggests interesting possibilities. It is difficult to imagine a simpler clock than a minecart with a "push always after x days" condition, and guided minecarts offer unprecedented control over the path of dwarves.

Fluid logic[edit]

Minecart logic outperforms fluid logic sufficiently to have mostly replaced it. However, the problem of automated fluid delivery may be best solved through some fluid logic techniques, and may suggest some stupid dwarf tricks for those that want to use the fluid capacity of minecarts to compute.

See Also[edit]

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