Possible error in 2nd ed spec of multiway demux (p. 24)

[philbangayan]

There may be an error with the way the multiway demux is specified in page 24 (section 1.4) of the second edition of the book. The function reads:

Input: in, sel[2]
Output: out
Function: if (sel==00)      then {a,b,c,d} = {1,0,0,0},
          else if (sel==01) then {a,b,c,d} = {0,1,0,0},
          else if (sel==10) then {a,b,c,d} = {0,0,1,0},
          else if (sel==11) then {a,b,c,d} = {0,0,0,1}

But this means that no matter what the input in is, the output on one of the lines would be 1. I think the function should instead read:

Input: in, sel[2]
Output: out
Function: if (sel==00)      then {a,b,c,d} = {in,0,0,0},
          else if (sel==01) then {a,b,c,d} = {0,in,0,0},
          else if (sel==10) then {a,b,c,d} = {0,0,in,0},
          else if (sel==11) then {a,b,c,d} = {0,0,0,in}

This way, if the output on one of the lines will be match the input, which could be either 0 or 1. I also notice this is more consistent with what's in the first edition.

[rleininger]

I believe you are correct.  The spec certainly doesn't agree with the truth table at the top of the page.

The corresponding specification from the 1st edition is:

The Dmux8way spec also has the same error.