I have a hex-to-decimal code I always carry inside my
programs as part of a math package for 64 bits (16 nibbles).

It converts up to 7 hexa bytes "23 86 F2 6F C0 FF FF"
to its decimal in 8 bytes "99 99 99 99 99 99 99 99".

Take a look at: http://www.ustr.net/files/x2d.asm
it uses exactly 90 code bytes, plus 24 bytes in the ram area
for the calculations. You can reduce it for only 8 bytes if
using only 16 bits instead 64, as you require.

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Wagner Lipnharski - Orlando, Florida
microcontroller website: http://www.ustr.net