Chris,

Look for movc instructions, note the address loaded into DPTR (or DPH/DPL individually). This is the start of a constant table. Pull the routine apart noting if the index in A is "bound" by anl instructions or other mechanisms to "discipline" the contents of the ACC. This will help you determine the number of elements in a table.

Look for movx instructions again noting the address loaded into DPTR and/or R0/R1. This will help you determine I/O and memory.

Note all Bit Flags and Bit ports to determine I/O and "condition" signals or strobes.

Follow interrupt sevice vectors into there routines. This will help you determine the operation of background processing.

Early in the code intialization occurs "pull" this apart and you will discover the nominal state and values of key process variables and I/O-memory states.

regards,
p