Honestly, I can't. As I said, I don't Keil (nor do I Raisonance, IAR, Tasking, and who-knows-what-else).

But, in short, yes, this IS different.

The long answer is, that every compiler of a high level language such as C assumes that it has full control over the resources - namely registers and memory allocation. But, for this IAP call snippet, you want to take this control over - you want to set up particular registers and place this function at a particular address. The mechanisms to achieve this are entirely specific to the given toolchain. There may be general similarities, but unfortunately the devil is in the details - e.g. in the "classical" compiler-assembler-linker model, the placement of a certain routine to a certain address is usually accomplished at the linker stage, but the way how to achieve this is again linker specific, and the way how the given routine is "marked" for the linker to know it has to handle it differently from other routies, is again toolchain specific.

I am sure this is easy enough for somebody who is proficient in Keil, as it is just a few assembler lines and their proper placement - but apparently none of those on this forum work with the P89V51RD2. This is why I "sent" you to the Keil forum.

JW