74138: Difference between revisions

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[[Category:7400 series|138]]
[[Category:7400 series|138]]
The [[74138]] (common variants 74LS138, 74HC138) is a 1-to-8-line decoder/demultiplexer in the 7400 series.
The [[74138]] (common variants 74LS138, 74HC138) is a 3-to-8-line decoder/demultiplexer in the 7400 series.
The decoder has one active high and two active low enables and is often used to calculate complex boolean functions.
The decoder has one active high and two active low enables and is often used to calculate complex boolean functions.
== 74138 Pinout ==
== 74138 Pinout ==
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{| class="tabular"
{| class="tabular"
! G1 || /G2a || /G2b || S2 || S1 || S0 || /Y0 || /Y1 || /Y2 || /Y3 || /Y4 || /Y5 || /Y6 || /Y7
! G1 || /G2a || /G2b || S2 || S1 || S0 || style="border-left:3px double;"| /Y0 || /Y1 || /Y2 || /Y3 || /Y4 || /Y5 || /Y6 || /Y7
|-
|-
| 0 || X || X || X || X || X || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 1
| 0 || X || X || X || X || X || style="border-left:3px double;"|1 || 1 || 1 || 1 || 1 || 1 || 1 || 1
|-
|-
| X || 1 || X || X || X || X || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 1
| X || 1 || X || X || X || X || style="border-left:3px double;"|1 || 1 || 1 || 1 || 1 || 1 || 1 || 1
|-
|-
| X || X || 1 || X || X || X || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 1
| X || X || 1 || X || X || X || style="border-left:3px double;"|1 || 1 || 1 || 1 || 1 || 1 || 1 || 1
|-
|-
| 1 || 0 || 0 || 0 || 0 || 0 || 0 || 1 || 1 || 1 || 1 || 1 || 1 || 1
| 1 || 0 || 0 || 0 || 0 || 0 || style="border-left:3px double;"|0 || 1 || 1 || 1 || 1 || 1 || 1 || 1
|-
|-
| 1 || 0 || 0 || 0 || 0 || 1 || 1 || 0 || 1 || 1 || 1 || 1 || 1 || 1
| 1 || 0 || 0 || 0 || 0 || 1 || style="border-left:3px double;"|1 || 0 || 1 || 1 || 1 || 1 || 1 || 1
|-
|-
| 1 || 0 || 0 || 0 || 1 || 0 || 1 || 1 || 0 || 1 || 1 || 1 || 1 || 1
| 1 || 0 || 0 || 0 || 1 || 0 || style="border-left:3px double;"|1 || 1 || 0 || 1 || 1 || 1 || 1 || 1
|-
|-
| 1 || 0 || 0 || 0 || 1 || 1 || 1 || 1 || 1 || 0 || 1 || 1 || 1 || 1
| 1 || 0 || 0 || 0 || 1 || 1 || style="border-left:3px double;"|1 || 1 || 1 || 0 || 1 || 1 || 1 || 1
|-
|-
| 1 || 0 || 0 || 1 || 0 || 0 || 1 || 1 || 1 || 1 || 0 || 1 || 1 || 1
| 1 || 0 || 0 || 1 || 0 || 0 || style="border-left:3px double;"|1 || 1 || 1 || 1 || 0 || 1 || 1 || 1
|-
|-
| 1 || 0 || 0 || 1 || 0 || 1 || 1 || 1 || 1 || 1 || 1 || 0 || 1 || 1
| 1 || 0 || 0 || 1 || 0 || 1 || style="border-left:3px double;"|1 || 1 || 1 || 1 || 1 || 0 || 1 || 1
|-
|-
| 1 || 0 || 0 || 1 || 1 || 0 || 1 || 1 || 1 || 1 || 1 || 1 || 0 || 1
| 1 || 0 || 0 || 1 || 1 || 0 || style="border-left:3px double;"|1 || 1 || 1 || 1 || 1 || 1 || 0 || 1
|-
|-
| 1 || 0 || 0 || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 1 || 0
| 1 || 0 || 0 || 1 || 1 || 1 || style="border-left:3px double;"|1 || 1 || 1 || 1 || 1 || 1 || 1 || 0
|}
|}


The [[NINA-003-006|NINA-03]] boards use a 74'138 for their peculiar register range mask.
The [[NINA-003-006|NINA-03]] boards use a 74'138 for their peculiar register range mask.

Latest revision as of 18:54, 30 October 2024

The 74138 (common variants 74LS138, 74HC138) is a 3-to-8-line decoder/demultiplexer in the 7400 series. The decoder has one active high and two active low enables and is often used to calculate complex boolean functions.

74138 Pinout

       .---v---.
  S0 --|1    16|-- Vcc
  S1 --|2    15|o- /Y0
  S2 --|3    14|o- /Y1
/G2A -o|4    13|o- /Y2
/G2B -o|5    12|o- /Y3
  G1 --|6    11|o- /Y4
 /Y7 -o|7    10|o- /Y5
 GND --|8     9|o- /Y6
       `-------'

Signal descriptions

It computes the following function:

  • G1, /G2a, /G2b, S2, S1, S0 are inputs
  • /Y0…/Y7 are outputs
G1 /G2a /G2b S2 S1 S0 /Y0 /Y1 /Y2 /Y3 /Y4 /Y5 /Y6 /Y7
0 X X X X X 1 1 1 1 1 1 1 1
X 1 X X X X 1 1 1 1 1 1 1 1
X X 1 X X X 1 1 1 1 1 1 1 1
1 0 0 0 0 0 0 1 1 1 1 1 1 1
1 0 0 0 0 1 1 0 1 1 1 1 1 1
1 0 0 0 1 0 1 1 0 1 1 1 1 1
1 0 0 0 1 1 1 1 1 0 1 1 1 1
1 0 0 1 0 0 1 1 1 1 0 1 1 1
1 0 0 1 0 1 1 1 1 1 1 0 1 1
1 0 0 1 1 0 1 1 1 1 1 1 0 1
1 0 0 1 1 1 1 1 1 1 1 1 1 0

The NINA-03 boards use a 74'138 for their peculiar register range mask.

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