Add & Subtract
This straight forward layout shows how A can be added to or subtracted from register S by linking two similar circuits. The upper circuit is an adder and the lower acts as a subtractor.
If the value of S drops below 0 or rises above 31 then it is out of range and the train returns on a combined underflow/overflow error line.
Operation
Enter the values of A (and S if necessary). Start the train from the correct input line depending on whether you want to add or subtract A from S. When the train halts, the result can be read from register S.
If A is set to 1, then the circuit acts as a Count Up (increment) or a Count Down (decrement) function.
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| Click layout to pause/run train | Click points to switch 0/1 | Click start circle to reset train/points |
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Lazy points switch between upper 0 or lower 1 branch lines Trains arriving on a branch line switch the point to that line |
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Sprung points allow branch line trains to join the main line All main line trains go straight ahead and never 'branch off' |