11C/15C keyboard layout and functions Message #14 Posted by Karl Schneider on 11 Mar 2006, 5:21 p.m., in response to message #13 by Valentin Albillo
Hi, Valentin 
Yes, indeed the layout and organization of the HP15C keyboard (based, of course, on that of the HP11C) is an absolute marvel of coherent thought and organization. Even after adding a substantial amount of functionality for the 15C, the grouping of functions on the keyboard was actually improved somewhat over the 11C. Note the following improvements on the 15C over the 11C:
 All statistical functions (except CLEAR SIGMA) are on the bottom row
 All three conversion functions are sidebyside
 Pi and its shift key are closer together
 x<>(i) and x<>I were replaced by a moreversatile "x<> "
Another bit of good thinking was to place SOLVE above the "divide" key, which is used for solving an exactlydetermined linear system of equations.
So, if one could revisit 19811982 to improve the HP15C (as well as other Voyagers, respectively), how could that have been done without changing its hardware or paradigm in any way? Fixed specifications include the following: Voyager packaging; 7segment, 10digit display; RAM; ROM space; microprocessor; and battery.
We've discussed this before, a few archives ago, with the question framed a bit differently. I can think of only the following improvements to the HP15C within the limitations I have specified:
Place LN and e^{x} on keys 12 and 13, rather than e^{x} and 10^{x}
This was implemented on the successor Pioneerseries models. Perhaps there was a pleasing symmetry with e^{x}, 10^{x}, and y^{x} sidebyside. Also, keycodes 11, 12, 13, 22, 23, 24, and 25 all had blueshifted inverses of transcedental functions (maybe that was the reason!). However, LN is just more useful than 10^{x}.
Show A, B, C, D, and E in program keycodes where appropriate (for labels and matrix identifiers), rather than the corresponding positional keycodes 11, 12, 13, 14, and 15.
This was implemented on the Pioneerseries HP20S, but might have run into issues of development time and ROM space for the HP15C.
Move CLx above the backarrow as a yellowshifted function, put "SHOW" or "MANT" as the blueshifted function, and perform "CLEAR PREFIX" as on the HP41 and the Pioneerseries models: by repressing the shift key.
Clearing a prefix key by performing a "no op" or "display mantissa" function was probably carried over from the LEDdisplay Spice models such as the HP34C, which had no annunciator for a shift key. I believe that considerable 34C microcode was ported to the 11C, which in turn was used in the 15C.
That's about it. For what the HP15C was, those are about the only feasible improvements I can think of  absolute perfection was nearly achieved. Certainly, a few other functions would have been useful, such xestimator (present on the HP10C and HP12C), y^{1/x}, x^{2}, and "ALL" display format. However, there just wan't available space, at least without resorting to key combinations that were arcane, unintuitive, or inconvenient.
BTW: What are the seven uses of the [+] operation? I can identify four, six, or eight, depending on how one is counting:
Two real scalars
Two complex scalars
Two matrices
One matrix and one real scalar (in either order)
STO + (real scalar to numbered register or matrix element)
RCL + (real scalar from numbered register or matrix element)
Best regards,
 KS
Edited: 11 Mar 2006, 5:28 p.m.
