Some basics to the clock ticks or time questions on the HP42S.
The HP42S programming language is similar to the HP41, but on the HP42S this programming language is rebuild by a high level interface in RPL, so synthetic programming isn't possible. Internally the HP42S is programmed in RPL with the objects known from the HP28 and HP48.
When I remember correct, there was a thought or discussion about native programming on the HP42S in the newsgroup comp.sys.handhelds in the early nineties or here in MoHPC. The thought was, every emulated HP41 command is saved as a RPL pointer object in RAM. When I write a program now, I can fill the program with dummy RPL pointers, then call the integrated memory scanner, go to the position of the program (but don't ask me how to find the address) and overwrite these dummy RPL pointers with own code. That's a sort of sythetic programming for the HP42S and for our further discussion let's asssume that this will work.
Now back to our time problem. Like all high end Pioneer calculators (veryfied on the HP17BII and HP27S) the HP42S has a 13 nibble (52 bit) tick counter at #50000 (=NEXTIRQ). The HP17BII and HP27S use this counter in connection with the timer2 content for the visible clock. So on all high end Pioneer calculators the content of =NEXTIRQ in connection with the timer2 content makes a good time base. When you write a very small piece of code using internal entries to get the ticks, how you want to handle them in the HP42S? Just calculate 2^52 on your HP42S and you'll get something like 4.5036E15 depending on the display format. Putting 13 nibbles into a 12 nibbles mantissa don't work without precision loss. OK, who's interested in a timer with 1/8192Hz resolution in most cases? So it's possible to pack a tick value with reduced precision into a float number. But remember, we are speaking here about pure assembler code packed into a code object patched by hand into the HP41 code. This object can't of course be edit with the internal editor any more.
I can only say very very hairy. Perhaps I forgot something very important, and there's a much easier way.
Because of that I like my HP48, and with restrictions the HP28S. On both calculators it's quite easy to add SysRPL or Code objects, but I don't want to discuss especially the techniques of SysRPL programming on the HP28S here.
Regards
Christoph