<sigh> how quickly they forget ...

Have a look at an OLD TTL databook. Not the current variety where every component is illustrated as a box, but the older ones, available in the library, that have the logic diagrams for things such as the 74LS185, which is a binary-to-BCD converter.

It might be well to bear in mind that a block that adds 6 (with carry) to each NYBBLE of data whenever the resepective input NYBBLE exceeds 9 will yield a BCD equivalent of the BINARY input. That condition is easily detected using the AND of bit 3 with the OR of bits 1 and 2.

Dick