As far as i'm aware of by reading
http://www.melabs.com/products/pbcis.htm
There's no ADCIN and direct acces to internal register, Variables are pre-defined B0... W1... and ,... and ... and

So you Must use PEEK POKE to write/read to/from internal register Adress and, and, and...

There's a huge difference between PBC and PBP. I don't have PBC here.. sorry

So only few code example @ melabs or other PBC user here could gives you some Hint. Look bellow
http://www.melabs.com/resources/samples.htm#pbc