HX-34 memory upgrade

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Por Manuel

Ascended (18160)

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27-12-2020, 16:16

Whatever you can read out with a programmer is most welcome Smile

Por popolon_

Master (163)

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27-12-2020, 17:20

I tried with R13 to +5v, but no change according to ramtest nor memtest. But i do not know if my added memory chips are real and not faulty.

Por popolon_

Master (163)

imagem de popolon_

27-12-2020, 19:45

@Manuel , the rom dump from TC531000P chip is problematic, as that is 1Mbit 28 pin ROM chip, and there seems to be not this kind of device type supported in minipro programmer.

Por popolon_

Master (163)

imagem de popolon_

27-12-2020, 21:18

Ok, there maybe R12 (right side from tcx2002) also that could be switched, have to check it tomorrow.

Por Manuel

Ascended (18160)

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28-12-2020, 01:10

OK, anything you can do to dump is fine and much appreciated! Smile

Por popolon_

Master (163)

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28-12-2020, 11:34

I dumped that mask ROM that was in socket:
https://github.com/popolonx/MSX_STUFF/blob/main/Toshiba_HX34...

Por popolon_

Master (163)

imagem de popolon_

28-12-2020, 12:28

According to HX-33 mainboard picture in wiki, it seems in HX-33 there is also same empty memory IC places, and these R11,R12,R13 resistors suitable to change (either +5V or GND).
This R12 (currently connected to +5V) is connected to line that connects TCX2001 (PIN 64) to TCX2002 (PIN 48).

Por popolon_

Master (163)

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28-12-2020, 16:06

yes, 128Kb memory was activated. Testram shows 128k mapper:
hx34_testram_output_128k_activated.jpg

and I tested with megaflashrom (flashrom 512k memory disable but MSXDOS2 booting), so 128K was really there.

128kb memory was activated by the R12, when that was moved from +5v to GND.
R11 was disabling keyboard when moved from +5V to GND
R13 I did not see any effect, so what could it be?
hx34_128k_mod.jpg

There is also R102/103 and R108/109 near FDD connector, but I did not manage to check where the signal goes exactly. R102/R108 is in place to transfer some signal (so it is not pull-up or pull down resistor). empty place R103/109 would be then connect this signal (R102/R108) to GND. But what would this be doing?
hx34_R102_103_108_109.jpg

Por Manuel

Ascended (18160)

imagem de Manuel

29-12-2020, 00:14

Does the original machine have a 64kB memory mapper? Or is it plain RAM? I expect the former.... otherwise you would have to have added the memory mapper as well.

Por gdx

Enlighted (4699)

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29-12-2020, 02:10

It seems that he added only two RAM and two capacitors to expand memory, so no doubt this MSX2 have originally 64kB mapped.

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