Siemens Simatic S7 Series Manual page 25

Optional Cartridges S7-200.CPUs.support.an.optional.memory cartridge.that.
provides.portable.EEPROM.storage.for.the.user.program..The.
cartridge.can.be.used.to.copy.a.program.from.one.S7-200.PLC.
to.a.like.S7-200.PLC...Two.memory.cartridge.sizes.are.available,.
64k.and.256k.bytes.
Two.other.cartridges.are.also.available..A.real-time clock with
battery.is.available.for.use.on.the.CPU.22.and.CPU.222..(CPU.
224,.CPU.224XP ,.CPU.224XPsi,.and.CPU.226.have.a.real-time.
clock.built.in.)..The.battery.provides.up.to.200.days.of.data.
retention.time.in.the.event.of.a.power.loss..Another.cartridge.is.
available.with.a.back-up battery only.
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