This MUST be read after reading Clonix's User's Manual

HEPAX+Advantage Who said it can't be?

Coming soon*
*Very soon*

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  Good mates

By March. '04 I was decided to face the task of emulating the so-called Holy Grail of the HP-41's modules. Namely, the HEPAX, and, more precisely, the Advanced HEPAX wich includes 16K RAM.

It's code is kinda esoteric. It can auto re-locate into any free page within the working range: i.e. pages #5 to #F for the 41C/CV or pages #6 to #F for the 41CX.

Apart from this "slippery" behavior it also performs the most dense utilization of the Bank-switching feature, installing its 16K ROM image into a single 4K page, therefore (ab)using of a unique 4 banks scheme.

It also implements instructions for Write-protecting RAM... in short: a real black beast, and a nice project for me! ;-)

After some attempt with parallel memory it becomes clear that serial memory was the way to go, which means lots of code will be required to handle the correct timing of the serial interface. As stated in the Clonix developement story, the available code memory was reduced to a mere 2Kbytes which leads to hours of scrunching routines ahead.

Finally, it fits the 2K limit and the first emulated Advanced HEPAX becomes a reality. Further more, it even outperforms the real HEPAX in some aspects: first, it can hold two extra ROM pages as it keeps the original Clonix ROM capabilities and second, its RAM memory does retain its contents even when the module was unplugged thanks to the use of Ramtron's Ferro-magnetic non-volatile serial RAM FM24C256.

As mentioned above, the main reason for the NoVRAM module to be developed was the interest in emulating the HEPAX, nonetheless, it was obvious that its posibilities beheld any RAM-Box emulation, thus several other RAM-Box OS are now available for configuration.