Jan:

Do note that the use of ASM code included into any part of a Keil C51 source file relegates the whole file to be processed as an ASM source as described by the others here. It is a total pain and probably one of the few dull spots on an otherwise very shiny compiler. The Keil behavior is somewhat unique in this regard and is completely due to how certain things are handled in their compiler implementation. You can take our word for it from the outset...If you want to retain your sanity and keep nice debugability of your C source code place your assembler stuff off in separate source files.

Please do not extrapolate to/from other MCU programming environments when considering how this works. There are plenty of other tool sets on other architectures that allow and handle in-line assembler in C code much the way tools on an PC would handle x86 code. I can cite the IAR tools on the AVR family and the CodeWarrior tools on the ColdFire family.

Michael Karas