Erase contents of SRAM

[R_G_B_]

please could someone  explain how to go about erasing the contents of a IS62C256

thanks

[wraper]

Why anyone would want to erase SRAM? Remove the power, LOL.

[rob77]

only battery backed SRAM would require erase...  ordinary SRAM is volatile, just remove power and all content is gone.

[pelule]

The  IS62C256 is a low power, 32,768 word by 8-bit. CMOS static RAM.
So, as alread said - just disconnect from supply and content is lost/erased.

[R_G_B_]

I have an old graphing style multi meter it's showing an error message hardware error I had a working one also to compare it with. After fault finding the circuit board I concluded it is probably a fault with the memory. I swopt the memory cards. The memory cards uses EEPROM. And So you can not save your user configuration here. it's stored on the SRAM next to the CPU on the main board when the multi Meter is switch on it loads the configuration.
From SRAM. Interesting as you have said the SRAM needs a battery to retain any data. However removing the power  does not result in loss of user configuration. I can not see any battery back up on this board. So I was asking my self if it's low power than how do reset it. If it's retaining the power in someway .

http://www.cypress.com/knowledge-base-article/erase-contents-sram

[wraper]

Unless there is supercapacitor or capacitor, there is no way to retain the data. Measure the voltage on the power pin when not powered. If there is none, your assumptions about data retention are wrong. If there is, then just short the power to the GND.

[SeanB]

Then there will be a small supercap or a 10 000uF 6V3 capacitor on the board. Simply remove all power from the board, and use a 100R resistor across the RAM power pins for 3 minutes to discharge it and erase it back to the random data it normally has on power up.

[pelule]

Before I would simply measure the VDD level at the SRAM, when the geas is süpowered off.
If ther is a backup-supply for the SRAM, should be able to measure it.

[R_G_B_]

Ok after checking the SRAM power is at zero volts. The memory cards uses a two EPROM  AT27C080

The CPU has built in 1K ram I have checked the supply rails and are all zero so I am at a loss where it is backing up the user configuration.

[rob77]

probably the CPU has an EEPROM where it's stored ? 

[Kjelt]

Look carefull if there is no small soic8 or similar 8 pin package somewhere. Easy overlooked but serial flash/eeprom is usually in those tiny packages.

[wraper]

Can you post a photo of the PCB?

[R_G_B_]

please see attachments

thanks guys

[Paul Moir]

U5 = 24LC01? That would be a 1 kilobit EEPROM.

[TiN]

Is it just me or U3 is cooked?
Also I'd clean that nasty crap around U8.

[JFJ]

... I swopt the memory cards...

There's a warning about swapping the memory cards, in post #3 HERE that might be relevant.

[R_G_B_]

There's no problem swooping memory cards


I identified the EEPROM:

24LC16B
In Production
The Microchip Technology Inc. 24AA16/24LC16B is a 16Kb I2C™ compatible Serial EEPROM. The device is organized as eight blocks of 256 x 8-bit memory with a 2-wire serial interface. Low-voltage design permits operation down to 1.7V with standby and active currents of only 1 µA and 1 mA, respectively. The 24XX16 also has a page write capability for up to 16 bytes of data. The 24XX16 is available in the standard 8-pin PDIP, surface mount SOIC, TSSOP, 2x3 DFN and MSOP packages, and is also available in the 5-lead SOT-23 package.

http://www.microchip.com/wwwproducts/en/en010819

[rob77]

now you can try to read it out first - keep the content... then erase the whole chip and give it a try... if it doesn't work then just write the original content back
you can do it with any micro or arduino or even bitbang it via a printer port on a PC (if you have a LPT).

[R_G_B_]

I manged to get into some kind of calibration or factory mode by wiggling the memory card.

i did try to calibrate but it was fiddly did not have enough hands  to hold the memory card while applying test probes
in channel 3 to calibrate the voltage now i can not get back in when wiggling the memory card might be i shorted something out with my hands that got me into this mode??

[mikerj]

The memory cards uses EEPROM. And So you can not save your user configuration here.

I don't follow your logic here; EEPROM is very commonly used to store configuration data?

[R_G_B_]

I managed to erase the contents  of the 24LC16B and replaced the IC. No success here. I am not sure why moving the memory card made it switch on now this method will not work.  I checked the soldering joints of the connector using a USB microscope all the joints seem fine. Seems that the connectors in the slot may not be making contact? interesting you do see some very slight fluctuations on the power supply when moving the memory card up and down. If this is the case why don't it switch on as it did before by moving the memory card?

intermittent fault or did i get lucky and some how entered some factory mode by accidentally touching something with my fingers?

I also tried cleaning all contacts and re soldering the connector joints.


Any help appreciated?
 



 

[CJay]

Is it just me or U3 is cooked?
Also I'd clean that nasty crap around U8.

Was thinking exactly that, looks like there's a nice little burn mark on it

[R_G_B_]

Is it just me or U3 is cooked?
Also I'd clean that nasty crap around U8.

that was a board i fixed a while back its burnt flux before i cleaned the board. I just used the same picture for a  different problem.

is it a possibility that I did actually enter a factory mode?

this menu is not normally present on start up.