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Algorithms, Math, and Physics

Transferring HP48 Programs to Emulators: A Personal Journey with ASCII Encoding

I’m sharing information on the structure of HP48 ASCII encoding, sourced from a FAQ available here. My intention is to detail a method I’ve found effective for transferring programs to emulators that do not support the Kermit transfer protocol but do allow for copy-pasting. This method involves encoding the program in ASCII format for transfer, then decoding it back on the emulator. It’s important to underscore that I am sharing this based on my personal experience and do not endorse or recommend this method due to the potential risks involved, including the loss of memory I experienced during my attempts.

Sending an HP48 GX Object via Email

Transferring an HP48 GX object via email can pose challenges if the object lacks an ASCII form, as is often the case for library objects. The solution I employed involves two programs, →ASC and ASC→. →ASC converts an object from the stack into a string, encoding each nibble of the object and its checksum into characters ranging from 0-9 to A-F. However, the object must reside in RAM; otherwise, a “ROM Object” error is encountered. To facilitate email inclusion, the resulting string is segmented by linefeed characters after every 64 characters.

ASC→ performs the inverse operation, converting a string back into its original object form. It’s crucial that the string remains unchanged during transmission, as ASC→ relies on the encoded checksum to verify the decoding accuracy. Any discrepancies result in an “Invalid String” error.

Implementation Details

The process involves two versions of ASC→: the first in HP48 user language, employing SYSEVAL for system object execution, and the second, a more compact and safer version, decoded by the first and then discarded. Despite the effectiveness of these programs in my scenario, it’s worth reiterating the importance of proceeding with caution due to the inherent risks of system-level modifications.

Installation process

My installation process was straightforward. I saved the necessary code into a text file named CONV, transferred it to the HP48 SX in ASCII transfer mode using Kermit, and verified its checksum before execution. This process enabled me to successfully install ASC→ and →ASC on my calculator, ready for use.

Checksum calculation and its implications

The HP48’s checksum function, while generally reliable, is not without its limitations. It’s designed to offer a unique identifier for objects, aiding in the verification of file transmissions. However, the rare possibility of identical checksums for different objects underscores the need for careful file handling and verification.

Conclusion

This journey through the process of transferring HP48 GX programs to emulators using ASCII encoding has been both challenging and rewarding. Despite the setbacks, including memory loss, the success of this method in my case highlights the potential for innovative solutions to compatibility issues. Nevertheless, this account serves as a cautionary tale of the risks associated with system-level interventions on these complex devices.

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