short circuit with disabled 3-bit decoder

[Pool_E]

i disabled a 3-bit decoder, but i somehow got a short circuit with it and an AND gate.

[UnsignedRobin]

There is always exactly 1 green output wire in a decoder. What the 'disable' does, is to turn that wire into red as well, so that all wires output red. The decoder is not 'truly' disabled, as it still outputs 'red' and not 'gray (nothing)'. Therefore, if you connect the output of a decoder to a wire, with a green signal, you get a short circuit.

[Pool_E]

Originally posted by UnsignedRobin:

There is always exactly 1 green output wire in a decoder. What the 'disable' does, is to turn that wire into red as well, so that all wires output red. The decoder is not 'truly' disabled, as it still outputs 'red' and not 'gray (nothing)'. Therefore, if you connect the output of a decoder to a wire, with a green signal, you get a short circuit.

so how do i get around this, and why does this not work the way it would seem to work by the word 'disable'?

[UnsignedRobin]

To solve that, you put an OR gate where the two wires connect. It doesn't completely disable it in the true sense, because to do that in real life, you need quite a lot of effort (the red signal is low voltage, the green signal is high voltage). To shut it down completely, you have to ground the signal somehow without side effects. This is called 'z-state' (if you want to look it up: Three-state logic, Pull-up resistor). Therefore the 'disable' on real life decoders just mean: do not output any green signal (usually one of them is always green).

[Pool_E]

Originally posted by UnsignedRobin:

To solve that, you put an OR gate where the two wires connect. It doesn't completely disable it in the true sense, because to do that in real life, you need quiet a lot of effort (the red signal is low voltage, the green value is high voltage). To shut it down completely, you have to ground the signal somehow without side effects. This is called "z-state" (if you want to look it up: Three-state logic, Pull-down resistor). Therefore the "disable" on real life decoders just mean: do not output any green signal (usually one of them is always green).

just seems a bit misleading, thanks!