I'm designing a low cost 8051 controller board which has to have RAM backup. Several people on this message bord say that a special RAM chip (from Dallas for example) is the best, but that is too expensive. Is it possible to make a simple analog (I mean with transistors and diods and NO chips) circuit with a backup battery. The docs of the RAM 65256 says that the ram has to get in Data Retetion mode by holding the "chip select" high while the battery takes over the supply.
I've tried to make a circuit that needed a diode in the Chip Select line but that did not work (to capacitive?). The signals after the diode where not like the signals before the diode (a fast scotkey diode).

Anyone have an idea that don't need a diode in the Chip Select line?