3.3v chip Ram expansion for A500+

avinitlarge · 11 June 2021, 00:26

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?

Thanks

Daedalus · 11 June 2021, 00:49

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.

torsti76 · 11 June 2021, 00:50

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.

avinitlarge · 11 June 2021, 00:56

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.

avinitlarge · 18 June 2021, 20:17

I had another look at it. After buying 5V chips, it still didn't work, I made a cock up when I reworked it to add the 3.3v regulator, D11 to the ram hadn't been reconnected. So now the 5V version works fine, Tried the 3.3V version and that works too

11 June 2021, 00:26	#1
avinitlarge Registered User Join Date: May 2016 Location: Rotherham Posts: 65	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? Thanks

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11 June 2021, 00:49	#2
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,369	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.

11 June 2021, 00:50	#3
torsti76 Registered User Join Date: May 2018 Location: Germany, Baden-Wuerttemberg Posts: 387	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.

11 June 2021, 00:56	#4
avinitlarge Registered User Join Date: May 2016 Location: Rotherham Posts: 65	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.

18 June 2021, 20:17	#5
avinitlarge Registered User Join Date: May 2016 Location: Rotherham Posts: 65	I had another look at it. After buying 5V chips, it still didn't work, I made a cock up when I reworked it to add the 3.3v regulator, D11 to the ram hadn't been reconnected. So now the 5V version works fine, Tried the 3.3V version and that works too

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