Paying back loans with irregular data

[brickviking]

I have an extra function on my calculator's TVM 'applet' that is rather useful: the ability to have more payments—or less—than the period payments that interest gets charged at. Simply put, I get the ability to set the number of compounding periods per year (C/Y) independently of the number of payments per year (P/Y). It means I can do neat things like get charged interest monthly, but pay fortnightly or even weekly, and the applet simply recalculates to suit. I haven't seen an equivalent on either of the HP calculators I tested (12C emulator/real 50G), nor do I know enough about finance to be able to write my own equivalent. Does someone know how to implement that in the 50G, or is there a pre-existing function in the 50g's stable of functions?

(Post 172)