OT: SRAM startup time and contents

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I have looked at Toshiba and Cypress data sheets and can find no reference.

What is typical startup times for SRAM?

Will the contents be all zeros after startup, or indeterminate, (i.e. can I cycle power to erase SRAM)? And if so, how long does power need to be off to insure all data has been lost?

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Startup time for the phsical SRAM should be about as fast as its power comes up.

My bet is that contents at startup are indeterminate. By and large, there is nothing in the SRAM designed to "reset" it to a known state on power up. Time to "erase" SRAM? Long enough. If you want it devoid of previous data, write something to it (all 0x00 or all 0xFF or all 0x5A or ...). This will probably be a lot faster and more certain.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Fri. Feb 25, 2005 - 07:50 PM
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I've found that some SRAM contained residue from data previously stored (but not perfect), depending on how long power was off. So if you want it blank, you have to write something.

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Thanks all.
I suspected as much, but hoped otherwise.

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mneary wrote:
I've found that some SRAM contained residue from data previously stored (but not perfect), depending on how long power was off. So if you want it blank, you have to write something.

It's usually not so much how long it was off but how low the voltage went. SRAM can retain data at pretty low voltages, where current draw ibecmes very low so even a small amount of capacitance on the supply can hold data for some time.