For those of you that have a HP15c LE, and remembering the previous post about cabling to repurpose a 12c to a 15c - now there is something that can be interesting to you!
The forum thread is here:
At the beginning of the post (already cited in the previous blog installment), they discuss the different HP15c firmware available, and they post three of them.
But later in the thread, there is a discussion on how to increase calculator memory in firmware, by patching the original ROM that is in every HP15c. The ROM adressed the available memory of the original calculator, but in the emulated system there is more memory! So there have been several attempts at increasing the memory by patching the original ROM in selected places.Someone has reached 128 registers (the original machine has 64), and there is an in-depth discussion on how to reach 192 registers. J-F Garnier even posts the ROM positions that need to be patched.
With that information, we have been able to create a patched ROM that allows for 192 registers. The firmware by default offers 94 registers and 99 non-allocated registers for programs and matrices. With this split, you could use 693 program steps. This is a screenshot of the MEM command, showing the above memory scheme. However, other splits are possible.