Static Random Access Memory (Sram); Memory System Operation And Precautions; Power Fail Restart; Normal Memory Operation - Siemens m50 Series User Manual

EPAC300-M50 SERIES USER'S MANUAL
The EPAC300-M50 series includes DRAM used to execute the traffic application
software. DRAM does not retain memory during power failures, and is therefore
reloaded from the FLASH drive after power failures.

3.6.3 Static Random Access Memory (SRAM)

The EPAC300-M50 series includes SRAM used as a "scratchpad" for temporary
data storage. The SRAM is backed by a capacitor during power failures for at least
30 days, assuming the controller has been powered for 20 minutes to allow proper
charging of the capacitor.

3.6.4 Memory System Operation and Precautions

3.6.4.1 Power Fail Restart

When the controller is powered, the traffic application software and intersection
data is automatically transferred from FLASH memory to DRAM. The traffic
application software executes directly from the DRAM. If power is lost for less than
500 mS, the power supply fills in missing line cycles and continues to provide
power for uninterrupted operation (Short Out). If power is lost for more than 550
mS, the controller is RESET and DRAM is lost. The controller will reload the traffic
application software and intersection data when power is restored (Long Out).

3.6.4.2 Normal Memory Operation

Once powered and running from DRAM, the traffic application software uses the
intersection data stored permanently in FLASH. SRAM is used as a scratchpad for
temporary storage of data. Changes to intersection data may be made via front
panel keyboard, or downloaded via communications. Because FLASH memory
requires extra time to store data permanently (like any storage drive), the FLASH
segment that is being stored is backed up in SRAM while that segment is being
written into FLASH. If power fails for more than 550 mS while FLASH is being
written, the unwritten data remains safe in the capacitor-backed SRAM until power
is restored. At that time, unwritten data is restored to FLASH within 30 seconds.

3.6.4.3 Memory Precautions

Be aware that any change to the FLASH drive, including loading software, loading
intersection data, changing passwords and keying in data, requires 30 seconds to
complete. If power is turned OFF before the FLASH is allowed to finish, and then
the controller remains unpowered until the capacitor discharges, the loaded data
will be lost. Worse, the FLASH drive sector that was "under construction" at the
time power was lost is corrupted, and must be recovered using the DCHECK utility.
To avoid FLASH corruption, simply be sure the controller remains powered for at
least 30 seconds after making any downloads or keypad changes.
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