Actually, if he has the 0x46 in single quotes, the compiler generates an error indicating that that is not a valid character constant.

This question was also posted to the Keil forum. There, I address the fact that A, B, C, R0-R7 and many other special names are used by the 8051 for registers. If you also use variables with these names, you must do something to differentiate them to the debugger.

Jon