HP-42S "reinterpretation"

[robert rozee]

(05-04-2015 09:07 PM)jch Wrote:  Robert, In the design using the PIC32MX170F256B, do you intend to use EEPROM as 'virtual' firmware memory, copying chunks of code to RAM before running them or as calculator continuous storage ?

The ARM way will even be more easily achieved using an already soldered device, like Teensy 3.1.

i've given little thought to how external EEPROMs would be used, beyond the need to provide some external (off-soc) storage. for the sake of robustness, it is desirable to not write to onboard flash on a regular basis. i do know that in some models of calculator casio, flash is used instead of battery-backed RAM, with the RAM copied into flash whenever the calculator is turned off, and retrieved when turned back on - this seems like a rather good scheme.

the "teensy" seems to provide no advantage over the PIC32MX170. both have identical quantities of RAM and flash, with comparable speed. but the PIC will run on two AA cells directly and has low-power modes, while the teensy needs 3v3. and the teensy cost 4x as much (us$20 versus <us$5).

the big winner with the PIC32MX170 is the ability to supply it as part of a kitset that almost anyone can assemble. and then there is MMbasic, which means the hardware can be tested before any calculator firmware is available.

my interest in this project is design of the hardware, presenting a simple concept that can be turned into something physical onto which the software can be loaded. this seems to be the stage that many complain the 43S is not at. i also wish to help prevent the project being killed dead by "feature creep" - no colour, no graphics, no bluetooth, etc. just a 'pure' 42S reinterpretation.


cheers,
rob :-)