This appeared in Motronic systems as they changed form 8051 Microcontroller based to the 8052.  For EPROMs of 32k file size or larger [27C265].

In this example,  I have highlighted [dark blue] s section of code from 0000h to 7EFFh.  At the bottom of the page, I have calculated the checksum  to be 3C7B.  

Stored at 7F00h, the same number 3C7B is stored. The checksum is a match. This is the basics of Checksum Verification. A routine in the code calculates the checksum  is compared to the stored checksum at 7F00h.  If there is an error in the EPROM's checksum, the EPROM code is faulty. A typical response might be to lower the rev limit and reduce ignition advance.  The engine warning light would be light.                     

What happens when you tune your car and change the maps? Alarms go off!  Your final step in editing should be to recalculate and update the stored checksum.