oldtoddler, This is how I would approch it:

BUSD VAR PORTD
A VAR BYTE
B VAR BYTE

LET A=10 (sets A bits 0..3 into %1010 = "10")
LET B=12 (sets B bits 0..3 into %1100 = "12")

BUSD = (B << 4) + A

Dave Purola,
N8NTA