Kontron VM62 - Manual (Page 36)

VM62(A) / VM42(A) User’s Manual Chapter 2 Functional Description
2.8 Data Retention for RTC and SRAM
Short term data retention for RTC and SRAM is gained with two Gold-Caps, each with a value of 0.22 Farad. In contrast
to Lithium cells, Gold-Caps do not require servicing. This short term backup is intended for short power failures or for
reconfiguring systems. An empty Gold-Cap needs approximately three hours to charge up, with backup times dependant on
the temperature, memory size and memory manufacturer tolerances. A well charged Gold-Cap provides a minimum of 10
hours backup time.
Laboratory tests at PEP indicate a typical backup time of 1 week for both 256kB and 1MByte SRAM plus RTC (typical
onboard backup current is 2
µ
A.
Long term data retention is made via the VMEbus 5V Stby line. With respect to the VM62(A) / VM42(A), this voltage
can drop to 2.5V, with the typical current via the 5V Stby being 30
µ
A at 3V.
Note
The VM42(A) / VM62(A) board can be removed from the system and then plugged in again without
losing any information. Data retention switches from the VME 5V Stby to the on-board Gold-Caps
automatically.
The on-board Gold-Caps are continuously reloaded via the 5V Stby line. The 5V Stby current is
typically 7mA for a few minutes when the Gold-Caps are at the beginning of the loading phase (fully
empty).
May 17, 1996 © 1995 PEP Modular Computers Page 2-21