HP-42S "reinterpretation"

[robert rozee]

the following expands on a comment i made in another thread that nobody seemed to want to run with...

i've been following the 43S thread with interest, and like others lamenting of the lack of progress. so i'm going to suggest a way forward, and present a simple hardware design that can easily be proven prior to anyone developing any calculator firmware.

we've seen a credit-card sized HP-25 emulator built using quite minimal hardware, and swiss micros are shipping their tiny HP-41 reinterpretation. the level of interest in both on the forums suggests to me that perhaps the time is ripe to look at someone doing a run of 'homebrew' HP-42S calculators.

the same keyboard solution as used on Chris Chung's "HP-25C Eumulator". a standard 1602 LCD module for the display (16x2 characters, HD44780 based). 2xAA cells for power directly to processor and LCD module. a PIC32MX170F256B (28-pin DIP package) to run it all, with 256k flash and 64k RAM on board. and running a derivative of Free-42 as the calculator firmware. if 256k of flash seems a little cramped, four additional 64k banks can be added using 24C512 EEPROMs (8-pin DIP packages). the first EEPROM can be used to hold the user programs (saved there after editing), while the remaining three can be used as needsbe for 'usercode' implementations of any functions that overflow from the processor's onboard flash.

i reckoned that minimal additional components would be required beyond PIC32, display module, and keyboard switches. the processor has it's own on-board clock generation and around 20 spare I/O pins to connect to everything. the keyboard would be charlieplexed:

   

and here is the neat bit... i've chosen pinouts such that the hardware will run MicroMite BASIC. so as it stands, one can flash MMbasic, attach a TTL serial terminal to the console pins (11 and 12), and code up some BASIC to test out the operation of the display, keyboard, and any attached EEPROMs.


positive comments?


cheers,
rob :-)