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[General] External SRAM addresses

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Fever

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Hi,

I have a few questions a SRAM external chip I want to use.

It has 20 address lines, from A0 to A19. It should mean that my address range is from 0x0 to 0xFFFFF. Since this is a 1024K-8bit array, I guess my real usable range is 0x0 to 0x3FF.

Does it mean I use only pins A0 to A9 ?
Does it mean that in this case the column decoder is useless, and I can tie to ground pins from A10 to A19 ?

Here is the datasheet of the product.
https://www.farnell.com/datasheets/2309579.pdf?_ga=2.42585318.296745661.1527512105-1452230848.1523286740&_gac=1.258948600.1527583888.Cj0KCQjw9LPYBRDSARIsAHL7J5lIBVD2HIJyJMFRU7K1q6pBJZ5nWnk0jlZZZ43O4Lngec2vJ7ux3uwaAmEwEALw_wcB

Thank you for your help.
 

I think you are confusing 1024 addresses (to 0x3FF) with 1024K addresses which goes to 0xFFFFF.

If you really only want to use 1K of the addresses, yes tie the unused address lines to ground but it seems a waste of a big memory if you only use a fraction of 1% of it's capacity.

Brian.
 

This is awkward. I don't understand how I missed that. Ok so no problem in the end. I want to use my 1M space so I will use all the addresses pins.

Just a little question. If the range is from 0x0 to 0xFFFFF, how can you achieve 2M with 20 pins on this chip ? (link below)

Is it because each address is 16bits and since your have 1M addresses you get 1M x 2 8bits ? If correct, is it used for special uses for example reading 16 bits at a time on a port so we can transfer data faster on a 16bits parallel bus device (like camera or LCD display) ?

Here is the datasheet : https://www.farnell.com/datasheets/2309580.pdf?_ga=2.239281216.296745661.1527512105-1452230848.1523286740&_gac=1.91224168.1527583888.Cj0KCQjw9LPYBRDSARIsAHL7J5lIBVD2HIJyJMFRU7K1q6pBJZ5nWnk0jlZZZ43O4Lngec2vJ7ux3uwaAmEwEALw_wcB

Thank you a lot for your time, I appreciate it.

Antoine
 

Hi,

read about BHE and BLE.

They control the byte wise access (2 x 8 bit) or the word access (1 x 16 bit).

You are free to use a 21st address line and generate BHE and BLE from it.

Klaus
 

Hi KlausST,

Oh yes I found the information in notes, in 2M x 8bits mode, pin 45 is used as A20.

Thank you very much for those explanations.

Have a great day.

Antoine
 

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