Per,

It is at least as much trouble/effort using the external memory space to attach peripherals, and probably more, as using SFR-space in the T51.

Keep in mind that the O/P was referring to a specific (T51) core rather than the general case. The core has inherent internal "examples" i.e. UART, Timers, etc. of peripherals mapped into SFR-space, while it has none in external memory space. It is slightly more involved mapping into external memory space because, among other things, it has to be decoded over a 16-bit bus which not only respond to MOVX instructions, but allow the use of the same internal direct-mode instructions that one would use in controlling the timers and UART. Setting and clearing bits in external memory space is a lot more trouble than doing it in directly addressable SFR-space.

The O/P has "gone away" long ago, probably because he was "corrected" by a faculty advisor, who pointe out the error of his ways. The information he initially provided was entirely inadequate. I suspect he and his colleagues have modified their approach and now have discovered answers to their questions.

RE