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Old 11 June 2021, 00:26   #1
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3.3v chip Ram expansion for A500+

I found a Kicad of a board I liked, https://github.com/blark/a500plus-chipram-expansion

I have 10 KM416V256BLT-7 which are the same pin out as the ones used in the link above but at 3.3v. I altered the Kicad pcb file added a 3.3v reg and changed the 5v line to the chips to 3.3v.

I built it all up today and boom, it didn’t work. It showed as .6mb then after a restart .12mb and now nothing.

So, could the problem be down to the voltage that is the issue or something else?

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Old 11 June 2021, 00:49   #2
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That chip isn't 5V-tolerant as far as I can see, so the input signals also need to be lowered from 5V to 3.3V, not just the power supply. If you didn't also include some level shifters, that'll be your problem.

I don't know if it's easy or possible to find compatible 5V-tolerant chips - maybe just try and find 5V parts for simplicity.
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Old 11 June 2021, 00:50   #3
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If not explicitly stated, the input lines of 3.3V chips usually are not 5V tolerant.

In the Amiga, everything is 5V, also address and data lines. Thus, you almost certainly killed the 3.3V RAM.

It can be done, but you'd need level shifters on all the I/O pins to translate between 5V and 3.3V logic levels.
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Old 11 June 2021, 00:56   #4
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Ah, that will be the problem then. I’m not going to bother with level shifters, I’ll just try and find the KM416C256B which is the 5v version.
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