Calculating the Checksum

[Georg Faustmann]

If the system is a Delco unit, then the Checksum on/off byte may be at
$0008, set this to $AA, the checksum (stored at $0006,$0007) should be the
total of all the bytes from $0008 to then end of the chip. 

In some cases the address of the checksum switch could be offset, eg $3008,
$8008.

Notes on how to find checksums:-

If you had access to an emulator with a Romwatch (real time trace) type
function where the actual bytes being read at that moment in time are
highlighted, then you can sit there and watch where the bytes start to be
sequentially accessed by the CPU (usually every 10 seconds or so), you can
then scroll down until you find out where they stop being accessed, and
will give you the start and end point of the checksum. Then add these range
of numbers up, and look for a 16 bit value that is the last 16 bits of this
sum, and search for this number outside of the checksum range, because it
can't be in the checksum area.

Georg