I've generally used a 1F capacitor that is charged through a diode and current limit resistor from the +5V supply. I then use a Dallas/Maxim 1210 to handle power switching. You also route the chip select to the RAM through the 1210 to prevent any reads or writes during power down. Write are obviously a problem, corrupting RAM. Reads are also a problem since the data lines would then attempt to power the powered down PIC, quickly discharging your battery or capacitor. Harold On Wed, 17 Oct 2001 08:37:28 -0700 John Waters writes: > Hi All, > > My microcontroller circuit has a 62256 (32Kx8) RAM chip, which is > used for > storing some important data I want to retain even when the power is > off. > What is the normal way to retain data on RAM? Is using a battery the > best > solution? If so, how do I turn on the battery "only" when the power > is off? > > Thanks in advance! > > John > > > > > _________________________________________________________________ > Get your FREE download of MSN Explorer at > http://explorer.msn.com/intl.asp > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu