Possible to Expand XP Memory?

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toml12953
Posts: 19
Joined: Mon Dec 20, 2021 4:55 am

Possible to Expand XP Memory?

Post by toml12953 »

I'm getting an Organiser II with 32K RAM. There's a model POS350 with 96Kb RAM. The hardware difference is that the POS350 has two extra 32Kb SRAM chips (Hitachi HM62256LFP-12T) These chips are still widely available. The solder pads for them are on the XP's main board. If I solder them in (they're surface mount) will the extra memory be available or are there software changes as well?
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MartinReid
Posts: 128
Joined: Wed Jan 27, 2021 3:44 pm

Possible to Expand XP Memory?

Post by MartinReid »

Dear TomL

Jaap has photos of the POS350 (here) but no mention of 'adding' the extra memory chips.. Although he does show a separate (PEEKB's) 'ROM' version 3.8 (here) and there are dedicated ROM images 3.6 and 3.8 (here) .

Andrew or MartinP might be able to cast more light on this...

Sincerely
Martin Reid
amenjet
Posts: 43
Joined: Sun Aug 22, 2021 6:56 am

Re: Possible to Expand XP Memory?

Post by amenjet »

MartinReid wrote: Tue Dec 21, 2021 11:09 am Dear TomL

Jaap has photos of the POS350 (here) but no mention of 'adding' the extra memory chips.. Although he does show a separate (PEEKB's) 'ROM' version 3.8 (here) and there are dedicated ROM images 3.6 and 3.8 (here) .

Andrew or MartinP might be able to cast more light on this...

Sincerely
Martin Reid
I'm not familiar with the P350, but any memory over 32K has to use the LZ bank switching circuitry. That is inside the Semi Custom Asic (SCA) and I doubt it was in the early XP models. I don't know if the LZ and LZ64 can have more memory added beyond 64K but maybe there is a memory sizing routine in the code. Anyway, what this does mean is that the code has to understand the bank switching scheme and perform switching in order to use the extra memory. So you'd need a machine with
a) Bank switching hardware
b) Code that uses bank switching

If your donor machine is an XP type machine then it probably can't use bank switching. An LZ might be able to be an LZ64, though, and it may be possible to add more than 96K to an LZ type machine by adding some large RAM chips, subject to the number of address lines the bank switching register has in the SCA.

Regards
Andrew
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