As already noted, when interfacing to a High-Level Language - any HLL - you must play by the Compiler's rules!

The Keil C51 compiler will use R6 and/or R7 to pass-in parameters - see: http://www.keil.com/support/m...assreg.htm

so you might as well take advantage of that!

Note that you do not have to preserve these registers - so, once you've received the passed-in values, you can do with them as you please!