Detecting presence of SD-card on HP-50g

[cahlucas]

Hi all,
For a program, I am making it is important to detect if there is an SD card in the HP-50g. How can I best do this in system RPL? As far as I can tell there is no special command for it. Something must be possible here because the built-in filer would not be able to work with an SD card if that function were not present. The program must therefore be able to detect with a flag (TRUE/FALSE) whether an SD card is present or not. I would like to use this function in my program. Sincerely, Karel.