how to build a 16-4 encoder using 8-3 encoders and OR gates?

Question

how to build a 16-4 encoder using 8-3 encoders and OR gates?

Answer 1

** Using the source for reference to the MM74H148 8 line to 3 line encoder,

the connections for a 16 line to 4 line encoder will be described.

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Three 2 input OR gates are required.

Call the lower priority encoder Encod1, and the higher one Encod2.



The 2 output A0's go to one OR gate to become the final A0 output.

The 2 output A1's go to a second OR gate to become the final A1 output.

The 2 output A2's go to the third OR gate to become the final A2 output.

The GS of Encod2 becomes the final A3 output.

When one or more lows are input to Encod2 it disables Encod1,

by connecting E0 of Encod2 to E1 of Encod1.

Connect the fixed enable; E1 of Encod2 to logic '0'

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0 to 7 of Encod1 are the final 0 to 7 lower priority inputs.

0 to 7 of Encod2 are the final 8 to 15 higher priority inputs

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The same principle will apply even if you use a different chip.

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Please ask should any clarification be required.

Answer 2

8 To 3 Encoder

Answer 3

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Use the enable inputs on the encoders (LS138 types). On the first, connect the 8 signal to a low true enable, on the second to a high true enable. Connect the 1-2-4 signals to both encoders in parallel. The first decoder will give you outputs for codes 0 thru 7, then the 8 signal will disable it for codes 8-15. The second encoder will be disabled for codes 0-7, then the 8 signal will enable it for codes 8-15. So you need no AND gates, just the 2 encoders. Be sure to tie the unused enables to hi or lo as needed.