Use 4 small EEPROM instead of 1

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mrtinb
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Use 4 small EEPROM instead of 1

Post by mrtinb » Mon Dec 04, 2017 11:35 am

Hi :)

I know I can use e.g. a 32K EEPROM in place of a 8K EEPROM, by just ignoring some pins.

But how do I go the other way? I have 4 8K EEPROMs I want to appear as a 32K EEPROM.

I've googled a lot with no answers. Does anyone have a great link to a description of this?

(I'm only talking about parallel EEPROMS)
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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PokeMon
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Re: Use 4 small EEPROM instead of 1

Post by PokeMon » Mon Dec 04, 2017 1:50 pm

Well this is in general easy.
An 8kByte E(E)PROM has 13 address lines (A0-A12) while the 32kByte requires 15 (A0-A14).
You can wire all parallel except the /CE input.

You need than additional an address decoder like 74LS138 and feed A13 and A14 to A+B input, connect C to GND and G1 to +5V and connect /G2 to the incoming /CE or /CS from the 32k EEPROM. The output Y0 to Y3 can than be used as /CE for the corresponding 8k EEPROM.
Anyway you would need a small board for all components.

http://www.ti.com/lit/ds/symlink/sn54ls138.pdf

The EEPROMS have to be programmed with the part of the 32k file and put into the correct sockets.
I think it would be much more easier to use a greater E(E)PROM with 128kByte for example only partly.
Less chips. A15 and A16 can be simply grounded then.

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Paul
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Re: Use 4 small EEPROM instead of 1

Post by Paul » Mon Dec 04, 2017 1:57 pm

You were faster than me again.
In theory, there is no difference between theory and practice. But, in practice, there is.

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