Decoder - Revision history

FoxFireFive at 06:22, 16 March 2026

2026-03-16T06:22:19Z

← Older revision		Revision as of 06:22, 16 March 2026
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	~~; '''Decoder'''~~		[[File:4bit-decoder.png\|alt=4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.\|thumb\|4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.]]A decoder is a circuit that takes a binary input and activates a specific output bit corresponding to that input. It is commonly used to select one element out of many, for example a cell in memory. A decoder always outputs a single bit. Effectively it's translating a binary value into a unary value.
	~~: In ''Logic World'', a '''Decoder''' is a circuit that takes a binary input and activates one specific output bit corresponding to that input.~~
	~~: It is commonly used to select one element out of many, for example a cell in memory.~~
	~~: The Decoder always outputs a single bit.~~
	~~: Effectively it's translating a binary value into a [[wikipedia:Unary_numeral_system\|unary]] value.~~
	: [[File:4bit-decoder.png\|alt=4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.\|thumb\|4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.]]

	== Construction ==		== Construction ==

	A ~~Decoder~~ is ~~one of the simplest circuits~~ to build.		A decoder is a fairly easy circuit to build.
	First, determine how many bits you need.
	The number of output bits from input bits is given by:		First, determine how many bits you need. The number of output bits from input bits is given by:

	:<math>o = 2^i</math>		:<math>o = 2^i</math>
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	:<math>i = \log_2(o)</math>		:<math>i = \log_2(o)</math>

	So, if you want 256 outputs, you will need a decoder with 8 input bits.		So, if you want 256 outputs, you will need a decoder with 8 input bits. Each output has a specific pattern of {{on}} and {{off}} bits coming from the input. The circuit is basically a number of [[AND Gate\|AND]] gates for each possible combination.
	Each output has a specific pattern of {{on}} and {{off}} bits coming from the input. The circuit is basically a number of [[AND Gate\|AND]] gates for each possible combination.

	Here are the steps to build it:		Here are the steps to build it:
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	When you become more experienced, you can skip unnecessary details and make it as simple as the screenshot above demonstrates. This design, optimized for speed and size, uses the trick of connecting wires from '''output''' pins directly to the required items, avoiding additional buffers and wire routing. On the screenshot below you can see the side view and how it allows it to make it compact.		When you become more experienced, you can skip unnecessary details and make it as simple as the screenshot above demonstrates. This design, optimized for speed and size, uses the trick of connecting wires from '''output''' pins directly to the required items, avoiding additional buffers and wire routing. On the screenshot below you can see the side view and how it allows it to make it compact.
			{{Todo\|Rewrite a bunch of this AI slop}}[[File:Decoder-side.png\|thumb\|center\|alt=Side view of the decoder\|Side view of the decoder]]
	[[File:Decoder-side.png\|thumb\|center\|alt=Side view of the decoder\|Side view of the decoder]]

	== Speed ==		== Speed ==
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	Decoders are used primarily as part of the following circuits:		Decoders are used primarily as part of the following circuits:

	[[RAM]], [[ROM]]~~<br>~~		* [[RAM]]
	[[Control Unit]]~~<br>~~		* [[ROM]]
	[[Multiplexer]], [[Demultiplexer]]~~<br>~~		* [[Control Unit]]
	[[~~Lookup_Table~~]]<br>		* [[Multiplexer]]
			* [[Demultiplexer]]
			* [[Lookup Table]]<br>

	== See also ==		== See also ==
	* [[Encoder]]		* [[Encoder]]
	* [[Lookup Table]]		* [[Lookup Table]]

N00basaurus: Changed the control unit link from CU to Control Unit

2025-10-06T05:09:19Z

Changed the control unit link from CU to Control Unit

← Older revision		Revision as of 05:09, 6 October 2025
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	[[RAM]], [[ROM]]<br>		[[RAM]], [[ROM]]<br>
	[[~~CU\|~~Control Unit]]<br>		[[Control Unit]]<br>
	[[Multiplexer]], [[Demultiplexer]]<br>		[[Multiplexer]], [[Demultiplexer]]<br>
	[[Lookup_Table]]<br>		[[Lookup_Table]]<br>

DjSapsan: /* Construction */

2025-09-12T22:55:30Z

Construction

← Older revision		Revision as of 22:55, 12 September 2025
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	So, if you want 256 outputs, you will need a decoder with 8 input bits.		So, if you want 256 outputs, you will need a decoder with 8 input bits.
	Each output has a specific pattern of {{on}} and {{off}} bits coming from the input. Here are the steps to build it:		Each output has a specific pattern of {{on}} and {{off}} bits coming from the input. The circuit is basically a number of [[AND Gate\|AND]] gates for each possible combination.

			Here are the steps to build it:

	* Place a row of input items.		* Place a row of input items.

DjSapsan: /* Construction */

2025-09-12T22:49:21Z

Construction

← Older revision		Revision as of 22:49, 12 September 2025
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	* Place a row of input items.		* Place a row of input items.
	* Connect each input bit to a NOT gate ~~to get its inverted value. And add~~ a Buffer to ~~pass~~ the ~~non-~~inverted value and match the delay with the NOT gate.		* Connect each input bit to both a [[Inverter\|NOT]] gate and a [[Buffer]].The NOT gate is required to have the inverted value and the Buffer is required to match the delay with the NOT gate.
	* Place a row of NOT gates to serve as the outputs.		* Place a row of NOT gates to serve as the outputs.
	* Go through each output NOT gate and connect them to the corresponding inputs (normal or inverted) to match its binary value. For example, the output corresponding to number 12 (binary 1100) should receive the following binary values:		* Go through each output NOT gate and connect them to the corresponding inputs (normal or inverted) to match its binary value. For example, the output corresponding to number 12 (binary 1100) should receive the following binary values:

DjSapsan: added "part of"

2025-09-10T16:43:51Z

added "part of"

← Older revision		Revision as of 16:43, 10 September 2025
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	The compact design above computes the output in 2 ticks.		The compact design above computes the output in 2 ticks.

			== Part of ==

			Decoders are used primarily as part of the following circuits:

			[[RAM]], [[ROM]]<br>
			[[CU\|Control Unit]]<br>
			[[Multiplexer]], [[Demultiplexer]]<br>
			[[Lookup_Table]]<br>

	== See also ==		== See also ==
	* [[Encoder]]		* [[Encoder]]
	* [[Lookup Table]]		* [[Lookup Table]]

DjSapsan: Removed behavior, as it's the same as the definition. + some tweaks

2025-09-09T18:37:40Z

Removed behavior, as it's the same as the definition. + some tweaks

← Older revision		Revision as of 18:37, 9 September 2025
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	; '''Decoder'''		; '''Decoder'''
	: In ''Logic World'', a '''Decoder''' is a circuit that takes a binary input and activates one specific output bit corresponding to that input ~~value~~.		: In ''Logic World'', a '''Decoder''' is a circuit that takes a binary input and activates one specific output bit corresponding to that input.
	: It is commonly used to select one element out of many, for example a cell in memory.		: It is commonly used to select one element out of many, for example a cell in memory.
	: ~~See also~~ [[~~Encoder~~]]~~, which performs the reverse operation~~.		: The Decoder always outputs a single bit.
	:[[File:4bit-decoder.png\|~~thumb\|right\|~~4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.]]		: Effectively it's translating a binary value into a [[wikipedia:Unary_numeral_system\|unary]] value.
			: [[File:4bit-decoder.png\|alt=4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.\|thumb\|4-bit decoder. Input on the left is 1110. The 14th output bit on the right is activated.]]
	~~== Behavior ==~~

	The ~~Decoder's~~ output ~~is always a single~~ bit ~~that corresponds to~~ the ~~input value, effectively translating a binary value into a [[wikipedia:Unary_numeral_system\|unary~~]] ~~value.~~


















	== Construction ==		== Construction ==
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	You can design a decoder in different ways. If you are building one for the first time, you may want to explicitly place each wire and gate to match the real electronic analog or to be visually understandable.		You can design a decoder in different ways. If you are building one for the first time, you may want to explicitly place each wire and gate to match the real electronic analog or to be visually understandable.

	When you become more experienced, you can skip unnecessary details and make it as simple as the screenshot above demonstrates. This design, optimized for speed and size, uses the trick of connecting wires from '''output''' pins directly to the required items, avoiding additional buffers and wire routing. In the screenshot below you can see the side view how to make it compact.		When you become more experienced, you can skip unnecessary details and make it as simple as the screenshot above demonstrates. This design, optimized for speed and size, uses the trick of connecting wires from '''output''' pins directly to the required items, avoiding additional buffers and wire routing. On the screenshot below you can see the side view and how it allows it to make it compact.

	[[File:Decoder-side.png\|thumb\|center\|alt=Side view of the decoder\|Side view of the decoder]]		[[File:Decoder-side.png\|thumb\|center\|alt=Side view of the decoder\|Side view of the decoder]]

Felipe: improve "see also" formatting

2025-09-09T18:21:36Z

improve "see also" formatting

← Older revision		Revision as of 18:21, 9 September 2025
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	== See also ==		== See also ==
	[[Encoder]]		* [[Encoder]]
	[[~~Lookup_Table~~]]		* [[Lookup Table]]

DjSapsan: construction and speed

2025-09-09T17:10:17Z

construction and speed

@@ Line 1: / Line 1: @@
 ; '''Decoder'''
-: In ''Logic World'', a '''Decoder''' is a circuit that takes a binary input and activates one specific output bit that corresponds to that input value.
+: In ''Logic World'', a '''Decoder''' is a circuit that takes a binary input and activates one specific output bit corresponding to that input value.
-: It is commonly used to select one thing out of many, memory addresses, or to enable particular parts in a circuit.
+: It is commonly used to select one element out of many, for example a cell in memory.
-: See also [[Encoder]], it's doing the same but in reverse.
+: See also [[Encoder]], which performs the reverse operation.
-[[File:4bit-decoder.png|thumb|right]]
+== Behavior ==

DjSapsan: First iteration of the decoder page

2025-09-09T16:11:48Z

First iteration of the decoder page

New page

; '''Decoder'''
: In ''Logic World'', a '''Decoder''' is a circuit that takes a binary input and activates one specific output bit that corresponds to that input value.
: It is commonly used to select one thing out of many, memory addresses, or to enable particular parts in a circuit.
: See also [[Encoder]], it's doing the same but in reverse.

[[File:4bit-decoder.png|thumb|right]]