Illumina file interpretation ATCG to AB

Question

[MichaelTrev]

I have a file for example:

SNP    TOP1&2    AB1&2

SNP1      GG       BB 
SNP2      CC       AA
SNP3      GG       BB 
.
.
SNP6      AC       AB   
SNP7      CC       BB
SNP8      AA       AA

Can someone explain me why first CC is AA in AB format, and another CC is BB? If I understand correctly, it is about the preceding and the following SNPs? Is there a map somewhere available? Or could someone write this to me, to check if I am translating correctly TOP1 TOP2 translators on AB1 AB2?