Manual

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 2µA.

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 30µA 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).