Our programmer software calculates the checksum of the data in the buffer.
P89LV51RC2 and AT89C55 have different buffer sizes. After you load the same hex file,
their device buffers actually are different. AT87C5133 and P89LV51RC2 have the same
buffer size (0000-FFFFH). You will get the same checksum after loading the same Hex
file to the same size buffer.