The BCD inputs are weighted like this:
Since 2,4,8,16,32,64 are pretty straight binary numbers,
it's easy to see why one BCD input signal connects to two
adder inputs in the schematic above... at least for me.
For 8 Bit binary to BCD conversion, you better use EPROMs,
Found some neat schematics in:
TTL Kochbuch, TI Germany, 1980,
Once there was another concept, called Excess 3.
Basically it looks like adding 3 to the BCD code.
Point is, that the book claims, that using this sort
of code simplifies decimal adder circuits.
If you happen to have 4 Bit binary adders,
converting BCD to Excess 3 and back is simple:
Converting BCD to Excess 3 by using logic gates:
Unfortunately, I had no example for converting
Excess 3 back to BCD by using logic gates.
Here we go:
Schematic for converting Excess 3 to BCD:
An alternative version for generating the B2 signal:
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(c) Dieter Mueller 2012