Hello and thanks for reading this message,

I am building a project using a 16c877 with a couple of 8-bit latches etc to interface to a 32kx8bit memory chip. I have managed to get this working OK, but I want to battery back this when the power is turned off.

Being naive I thought that just using a couple of diodes to the RAM power supply pin would be enough to do the job...No chance it draws 15-18mA from the backup supply when the main supply is off, this despite the whole circuit drawing only 10 - 12mA in normal operation!

I have since found out that these static RAM chips have to be set into a 'data retention mode'. Now can somebody please point me in the direction of a suitable circuit (simple if possible) which will reliably set the RAM chip into this mode on power down?

PS the RAM chip I have is Goldstar type GM76C256L-10 (100nS?) which I presume is a generic type.

Thanks again for your time... Barry.