PiXtend V2 -L- Hardware Manual
6.2.5.Retain System
PiXtend V2 -L- has a retain / persistent memory
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. In the event of a voltage drop
(fluctuations in the supply network, power failure, etc.), important data can be saved.
The Retain system is independent of the software used (CODESYS, C programs, Python
programs ...) and the Linux operating system. Retain data is cyclically transferred to the
microcontroller by any user software running (which depicts the process image of PiXtend
V2 -L-) on the Raspberry Pi.
The PiXtend microcontroller monitors the voltage at the supply input ("VCC"). If the retain
system is activated and the supply voltage falls below 19 V DC, the controller changes to
the safe state and stores the retain data. In the time from the detection of the undervoltage
to the complete storage of the data, PiXtend V2 -L- and the Raspberry Pi are fed from an
internal capacitor.
After the power supply has been restored and the PiXtend system is restarted, the
previously backed up data is provided by the microcontroller and can be retrieved in the
user program.
The Retain system can only be activated and used if a nominal supply voltage of 24 V DC
is used. If, for example, PiXtend is operated with 12 V DC, the Retain memory can not be
used and is disabled.
Property
Value
Comment
Type of memory
Flash EEPROM
the PiXtend microcontroller
Number of storage cycles
min. 10,000
Memory size
64 Bytes
voltage threshold
19 V DC (+/- 0.6 V)
between VCC and GND
Nominal supply voltage
24 V DC
to benefit retain
Max. Input power
about VCC
10 W
for the guaranteed storage of
all data
Table 10: Technical data - retain system
Retain functionality should be disabled when it is not required.
For more information on using the retain system, see the PiXtend V2 Software Manual.
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also called remanence memory
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