[BioC] how to read in affy snp 500K arrays

[affy snp]

Dear list,

I am analyzing a bag of Affy SNP 500K arrays and would like to
know which package can be used to read in the raw .CEL files
and get the intensity values. In other words, I am looking for
the function like:

library(affy)
mydata <- ReadAffy()
eset_rma <- rma(mydata)

provided by affy package to analyze affy gene expression data.

Thank you very much!

Sincerely,
       Allen