NMS 8220 Replace the application rom

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By Caliostro

Resident (54)

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16-05-2021, 23:50

Hi, i have a NMS 8220 and I wanted to get some experience, I try to replace the internal MBM27128 application ROM, with a M27C512, I managed to run a 16K game, from address C000, but I can't get bigger games to work, I have tried to connect A14 to Z80, VPP at ground, CE at CS1, CS2, CS12 (default), nothing works ....
Where am I wrong?

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By gdx

Enlighted (4385)

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17-05-2021, 02:47

If 32kB is enough for you, just replace the MBM27128 with a M27C256 and add the A14 signal (pin 27). The track has to be cut to do this.

For 64kB, replace the MBM27128 with a M27C512, I think you have to remove the J1 jumper to put the A15 signal in the pin 1, cut the /CE track and replace it (pin 20) by /SLT33 signal then cut the /OE track and replace it (pin 22) by Vpp (for the J1 jumper), and add also the A14 signal (pin 27) of course.

See the service manual in the wiki! Also wait for the opinion of other people because I am not an expert.

By Caliostro

Resident (54)

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17-05-2021, 09:44

Thanks for the reply, where can I find SLT33?

By gdx

Enlighted (4385)

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17-05-2021, 10:12

This signal is originally connected to the /CE pin. (See the service manual)
Maybe you can leave it as is and put Vpp to /OE. I think it doesn't matter that the signal of these two pins are reversed. It would avoid cutting a track.

By Caliostro

Resident (54)

Caliostro's picture

17-05-2021, 10:30

does not work

By gdx

Enlighted (4385)

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17-05-2021, 13:01

I advised you to wait but try with /RD to the pin 20 instead of Vpp (sorry for the mistake) and /SLT3-3 to pin 22.

Why do you want a Rom of 64kB?

By Caliostro

Resident (54)

Caliostro's picture

17-05-2021, 14:01

Because I only have 27C512 and because I want to learn new things ...
now it says the missing operands in 0
I try to change ROM, but at least something happens

By Caliostro

Resident (54)

Caliostro's picture

17-05-2021, 14:53

I had not inserted the dip well, with these connections, msx does not turn on

By Caliostro

Resident (54)

Caliostro's picture

18-05-2021, 08:48

I installed a 27C512 in the fender spc-800 too and it works (configuration 27064), but now i'm wondering, is it possible to add an instruction to skip this rom (press esc while booting for example)

By Pencioner

Scribe (1405)

Pencioner's picture

18-05-2021, 10:35

Caliostro wrote:

I installed a 27C512 in the fender spc-800 too and it works (configuration 27064), but now i'm wondering, is it possible to add an instruction to skip this rom (press esc while booting for example)

You have to modify the rom and make it read keyboard and exit if the key is pressed

By Caliostro

Resident (54)

Caliostro's picture

18-05-2021, 10:42

is it possible to add a line in the hex file?

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