Creating ROM for vg8235 from nms8245

By o.geerdink

Hero (539)

o.geerdink's picture

14-09-2019, 11:09

Hi Guys,

I need some help with this. I thought it was just a matter of copying the ROM but I read about all kinds of eprom types and voltages. I want to dump the disk-rom from my nms8245 into a blank eprom. And put that rom inside a vg8235.

I have several eprom:

AM27C512-255DC
27c256-15
m2732A

In a manual about installing it the eprom is 27128-25

I don't know which chip I should use, to be honest this is much more complicated than I thought. I use toeprom 1.9 and it boots, can call toeprom etc. Who ever used this thing?

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By mohai

Paladin (833)

mohai's picture

14-09-2019, 13:09

I never used Toeprom, but I think I can give you some advice.
I guess you have a 8235 with big board and 3 Eprom chips on it.
If you do kot want to keep the existing DISKROM, then you can re-use the chip. It should be a 27c128 type, for 16 Kb.
All you need to do is to erase it with UV light (Or expose it to the sun for several days... ).
Then write it with your favourite Eprom writer.

If you do not have a spare 27c128, then a bigger one can be suitable. Make sure you choose the same speed or faster (27cxxx-25 or 20 or 15 or so...), and write the ROM file several times, until you fill the chip up (this is because chip pinout compatibility).

I used a 27c512 for mine, and it worked fine.

By o.geerdink

Hero (539)

o.geerdink's picture

15-09-2019, 07:56

Thanks for your help so far.

I rather not clean the old chip before I got a working new, don't want to brick the machine.

So I can use the AM27C512-255DC. To be honest I just don't understand the part about filling the chip up. You mean with chip compatibility that the msx can send unpredictable signal on the address linkes not used by msx (causing it not to select the first 16KB page on the rom?).

Toeprom asks me for a voltage and address range. I thought that should be 4000-7FFFF. Voltage for this chip is 5v right? Can you really toast them by sending to high voltage?

I can put the chip in the programmer in 2 ways, I don't know what side is up to be honest Big smile. The manual of the toeprom is clearly for people who know what they're doing..not me.

I'll try to cook one and see what happens. Nishi

By o.geerdink

Hero (539)

o.geerdink's picture

15-09-2019, 08:30

I can select the eprom type. I inserted a 27C256 chip but if I select it the toeprom thinks it goes from 4000-BFFFF so I select 27c128. Now it expects to write 4000-7FFF and you're saying I need to do that twice so on the chip the second 16KB block is equal to the first.