How do you determine a 71B memory-mapped I/O device address?

[Giuseppe Donnini]

The best place to start, in my opinion, would be Nathan Meyers article "Soft Configuration Enhances Flexibility of Handheld Computer Memory", published in the July 1984 issue of the Hewlett-Packard Journal (p. 10-13).

The most advanced and detailed treatment can be found in the HP-71 Software Internal Design Specification. Chapter 2 of the first volume, entitled "System Startup and Memory Configuration", gives a general overview, while all the gritty details can be gleaned from the actual source code and its comments in the third volume (starting at address #10192h).