Jörg,

A good thread for an interesting topic based upon a good practical question.

I concur with Peter on this.

I would expect any of the architectural elements which propagate from the original intel '51/'52 to comply with the stated behaviour for the use of Direct Addressing as defined within intel's MCS 51 Microcontroller Family Users Manual:

"Direct Addressing

In direct addressing the operand is specitied by an 8-bit addreas field in the instruction. Only internal Data RAM and SFRs can be directly addressed."

As a bi-directional holding reg the SBUF is not really that different from other SFR's such as the Timer Reload registers, or Port SFR's.

regards,
p