If you really want to write a compiler, a good start is the "small-C", a C compiler writtten in the C language, originally written for the intel 8080 processor. The source code is available on the internet. Later, this code was ported to (both) Motorola 68000 and 68HC11 processors. Just look for "+small +C +compiler" (a search in yahoo will find about 170 thousand matches :o) )