Siemens Simatic S7 Series Manual page 27

Super Capacitor.
.
An.optional.fan-out connector.allows.field.wiring.connections.
to.remain.fixed.when.removing.or.replacing.a.CPU.22.or.
CPU.222..The.appropriate.connector.slides.into.either.the.input,.
output,.or.expansion.module.terminals.
Optional Fan-out Connector
for CPU 221 or CPU 222
CPU.224,.CPU.224XP ,.CPU.224XPsi,.and.CPU.226.do.not.have.
an.optional.fan-out.connector..Instead,.their.terminal.strips.are.
removable..
A.super capacitor,.so.named.because.of.its.ability.to.maintain
a.charge.for.a.long.period.of.time,.protects.data.stored.in.RAM.
in.the.event.of.a.power.loss..
The.RAM.memory.is.typically.backed.up.for.50.hours.on.the.
CPU.22.and.CPU.222.and.for.00.hours.on.the.CPU.224,.CPU.
224.XP ,.CPU.224.XPsi,.and.CPU.226..
Super Capacitor
26
CPU 224, CPU 224XP, and CPU 226
Removeable Terminal Strip
EEPROM
RAM
(Non-volitle)
(Volatile)
Executed
Program
Program
Backup
Current
Data
Parameters
Memory
Bits,
Timers,
Counters
Field Wiring
Connector Posts
Optional EEPROM
Memory Cartridge
(Non-volatile)
Program
and
Parameters