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Electronics => Repair => Topic started by: giosif on March 03, 2019, 08:38:52 pm

Title: How to read contents of PCF8570 SRAM
Post by: giosif on March 03, 2019, 08:38:52 pm

Hi all,

I am looking to replace the button cell battery that powers a Philips PCF8570 SRAM IC (part of a board from a PM5139 function generator).
The battery isn't dead, but don't know how much life it's got left in it, so I would like to put in a new one.
However, I would first like to back up the contents of that IC, just in case I end up cutting off power to it.
Any ideas how I could achieve that?
The trusty TL866 doesn't seem to support the said IC.

Thanks!

Title: Re: How to read contents of PCF8570 SRAM
Post by: amyk on March 04, 2019, 04:08:43 am

I briefly looked over the service manual (https://isurplus.com.au/manuals/Philips%20PM5193%20Service%20Manual.pdf) but it doesn't appear to mention calibration constants are stored in it. In any case, if it reads the contents upon power-up or entering specific modes, then a logic analyser connected to it should be able to capture the data. There's only 256 bytes, it's not very large.

Title: Re: How to read contents of PCF8570 SRAM
Post by: giosif on March 04, 2019, 06:23:26 pm

Thanks for that, but the product is the PM5139, not PM5193!
In any case, the idea with the logic analyzer still stands.
I guess I was looking for an easier (read "lazy") way.  :)

Thanks again!

Quote from: amyk on March 04, 2019, 04:08:43 am

I briefly looked over the service manual (https://isurplus.com.au/manuals/Philips%20PM5193%20Service%20Manual.pdf) but it doesn't appear to mention calibration constants are stored in it. In any case, if it reads the contents upon power-up or entering specific modes, then a logic analyser connected to it should be able to capture the data. There's only 256 bytes, it's not very large.

Title: Re: How to read contents of PCF8570 SRAM
Post by: orbanp on March 04, 2019, 10:04:46 pm

Here is the datasheet for the RAM in question:
https://www.nxp.com/docs/en/data-sheet/PCF8570.pdf (https://www.nxp.com/docs/en/data-sheet/PCF8570.pdf)

Here is an Arduino sketch for an I2C-scanner:
https://playground.arduino.cc/Main/I2cScanner (https://playground.arduino.cc/Main/I2cScanner)

I am sure it would not take much to modify the code to read (and/or program) the content of the RAM.
It is also possible that there are other I2C sketches doing similar things, I did not look that hard.

Regards, Peter

Title: Re: How to read contents of PCF8570 SRAM
Post by: giosif on March 06, 2019, 07:56:18 pm

Thanks, Peter!

In the meantime, I read the user and service manuals and I'm pretty sure the SRAM stores only instrument settings, not calibration data.
In fact, the calibration is all analog (i.e. adjusting various trimpots).
That said, I'd still like to give it a try at reading the contents of the SRAM IC, even if just as an exercise for the next equipment that might store its cal data in a similar IC.

Cheers!

Quote from: orbanp on March 04, 2019, 10:04:46 pm

Here is the datasheet for the RAM in question:
https://www.nxp.com/docs/en/data-sheet/PCF8570.pdf (https://www.nxp.com/docs/en/data-sheet/PCF8570.pdf)

Here is an Arduino sketch for an I2C-scanner:
https://playground.arduino.cc/Main/I2cScanner (https://playground.arduino.cc/Main/I2cScanner)

I am sure it would not take much to modify the code to read (and/or program) the content of the RAM.
It is also possible that there are other I2C sketches doing similar things, I did not look that hard.

Regards, Peter