Author Topic: Possible NC200 internal expansions  (Read 841 times)

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Offline PulkoMandy

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Possible NC200 internal expansions
« on: 17:40, 05 December 20 »
Hi,
Somehow I'm looking into the NC200 internal design today...


Things I noticed:
- The memory mapping registers allow for 1MB of internal ROM, 1MB of internal RAM, and 1MB of PCMCIA space. Of course a lot of that is unused (there is only 128K of internal RAM for example).
- On the NC200 motherboard (http://www.cpcwiki.eu/imgs/c/c2/NC200_PCB_Top_Rev32272.jpg) I see a missing IC under the PCMCIA port and under the RAM. The label on the PCB says it's for an https://datasheetspdf.com/pdf-file/535384/Hitachi/HN62314B/1 ROM. It seems https://datasheetspdf.com/pdf-file/64317/SanyoSemiconDevice/LE28FV4001T/1 would be flash memory with a compatible pinout. Anyone already tried this? Where will the chip be available in memory?
- Likewise, it seems that the RAM could be replaced with a larger one (https://www.distrelec.biz/Web/Downloads/_t/ds/62WV2568ALL_BLL_eng_tds.pdf seems to be a compatible 256K one), would this work?


Any idea or am I the first one to consider all this?

Offline Bryce

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Re: Possible NC200 internal expansions
« Reply #1 on: 18:58, 05 December 20 »
To find out where the flash would be mapped you'll have to work backwards from the Chip Enable / Output Enable pins of the chip and see what address lines would trigger it/them.

Bryce.
 

Offline robcfg

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Re: Possible NC200 internal expansions
« Reply #2 on: 19:03, 05 December 20 »
That's very interesting!


Is it only the NC200, or can the NC100 and 150 be upgraded as well?


I see on the NC150 an empty place (IC305) for a 43257 (256K-BIT CMOS STATIC RAM 32K-WORD BY 8-BIT), which is populated on the NC100.


I'm not sure if the original code would detect and make use of it, but it would be nice to see how far can we take these machines! :D

Offline PulkoMandy

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Re: Possible NC200 internal expansions
« Reply #3 on: 19:42, 05 December 20 »
On the NC100/150, there is space for two RAM chips: IC304 and 305. I think there qare two configurations: either with 2 28-pin chips, or one single larger 32pin chip.


Either you get two 32K chips (total 64K) or a single chip, which is 64K on the NC150, but maybe it can be upgraded too. I think this could fit: http://www.farnell.com/datasheets/1064284.pdf


Same thing, difficult to know if all the address bits are wired on the PCB, and if they are not, if they can be added with some extra wires. That depends on the behavior of the ASIC which manages the memory: does it output all 6 bits from the memory mapping register when accessing the internal memory, even if they are unused, or does it filter them out?


Also, the high 2 bits of the memory mapping registers have only 3 possible values: internal ROM, internal RAM, PCMCIA. What happens if you set it to the 4th undocumented value? Can we use that to further extend the address space?


Anyone has a schematic of the NC100 or NC200?

Offline robcfg

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Re: Possible NC200 internal expansions
« Reply #4 on: 21:02, 05 December 20 »
I haven't found any schematics, most probably because they weren't manufactured by Amstrad but built and customized for different clients by Nakajima.


Which is a pity, as there was no info on their now defunct web page and I don't know who could actually still have some design documents or schematics.

Offline PulkoMandy

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Re: Possible NC200 internal expansions
« Reply #5 on: 21:23, 05 December 20 »
What's strange is https://www.cpcwiki.eu/index.php/A_surgical_guide_to_the_Amstrad_NC has pinouts for all the chips (including the custom one) and says this:

Quote
I  belief  you  can put some bigger RAM-chip in the circuit, but there is nothing about that in the  electronic  diagram!

So this guy must have had access to some schematics. But he didn't share them :(