RAMBox for the HP-42S



#2

Hi!

When I visited the HPCC in London this summer Tony Duell showed me a RAMBox for the HP-41C(V/X). Now I wonder, have anyone tried building such a thing for the HP-42S? Or could anyone hardware oriented judge whether building a RAMBox for the HP-42S would be feasible?

The idea would be to add 32K RAM in the place of the additional ROM and make this RAM programmable from a PC. (Another option could be to use a 32K RAM card from the HP-48SX and use a HP-48 to "program" it). Using the XFCN hook this could be a way to add memory that is both programmable in assembler and possible to call from RPN programs...

Regards,


Erik Ehrling (Sweden)


Homepage:http://w1.322.telia.com/~u32220482/index.html


#3

I don't know if you've seen the posts or not so maybe this is old news to you but; a couple of people have replaced the 8k chip in the 42 with a 32k which is pinned the same. The problem is that it is not removeable or accessable by the 48, except that you could probably write a routine for the 48 to read signals from the 42. The reverse is sadly, not true as far as i know.

Wouldn't it be great if the much maligned (but not yet seen) 33s turns out to have a back door that HP forgot to plug which allows communication with mass storage?


#4

> I don't know if you've seen the posts or not so maybe this is old news to you but; a couple of people have replaced the 8k chip in the 42 with a 32k which is pinned the same.

Yes, I have indeed seen the posts regarding the 32K upgrade of the HP-42S (and have performed this upgrade to two of my HP-42S's).

However, what I was speaking about was a slightly different idea, where RAM is attached, not to the ordinary RAM position, but rather to the position of the additional ROM. This memory area has the benefit of, at least theoretically, being much more suited to programming in saturn assembly than the ordinary 8/32K RAM.

However, you would probably not like to enter more than very short programs by hand - therefore the RAMBox would need to be programmable from a PC (or some other device).

Best regards,
Erik Ehrling

#5

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!

b) Issues:

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)


#6

> 1) Standby power controller, there should be Chip Enable signals controlled sometimes from the HP42 (Saturn), and sometimes from the outside...

Hmmm... I might be somewhat naive, but isn't this issue already handled by the RAM Cards for the HP-48SX/GX?

> 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...

We do have Emu42 which certainly would be very useful for this. However, remember that my idea was to use this for the ROM area, i.e. the RAM that I am speaking about here would therefore be read-only once installed in the HP-42S.

Best regards,
Erik Ehrling


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