|Phantom: RAMBox for the HP-42S|
Message #4 Posted by Andrés C. Rodríguez (Argentina) on 7 Oct 2003, 12:37 p.m.,
in response to message #1 by Erik Ehrling (Sweden)
A RAM chip that could be mapped "to the outside", so it can be logically detached from the HP42 while it is off (sleeping), and "dumped" via a serial or USB connector (somehow in the manner of the flash memory keyrings) to a PC... and then loaded from the PC with a memory image... and then reverted to the inside just before the calculator is about to wake up...
a) May be a good idea!
b1) Standby power controller, there should be Chip Enable signals controlled sometimes from the HP42 (Saturn), and sometimes from the outside...
b2) The memory images would be difficult to edit or "compartimentalize", in some manner this would be similar to the WALL (Write All magnetic card) function on the HP41... not very frequently used. This could be solved with an emulator running on the PC which can read, understand, modify and save an HP42 memory dump...
b3) As the RAM is CMOS Static and a "standard" part, other timing and control issues could be solved.
c) The technique of using a block of memory initialized from one device and then addressed by other as if it was its own memory was called Phantom Memory. It was used for microcode loading (or control store programming, for those who don't like the microcode-microprogram terminology), for boot ROM emulation in the Commodore Amiga 1000, and in some 386 PCs some 12 years ago, to "upload" the image of 8-bit wide ROM in a 16 or 32 wide bit memory page, and so obtain performance benefits from bus usage (and also from better access time on DRAM than in ROM)