Motorola MVME162P-242, Installation And Use Manual

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Functional Description
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If the voltage of the backup source is lower than two volts, the CR2032
blocks the second memory cycle; this allows software to provide an early
warning to avoid data loss. Because the second access may be blocked
during a power failure, software should do at least two accesses before
relying on the data.
The MVME162P2 provides jumpers (on J14) that allow either power
source of the CR2032 to be connected to the 5V STDBY pin or
to one cell of the onboard battery. For example, the primary system backup
source may be a battery connected to the 5V STDBY pin and
the secondary source may be the onboard battery. If the system source
should fail or the board is removed from the chassis, the onboard battery
takes over.
!
Caution
For proper SRAM operation, some jumper combination must be installed
on the Backup Power Source Select header (refer to the jumper
information in Chapter 1). If one of the jumpers is set to select the battery,
a battery must be installed on the MVME162P2. The SRAM may
malfunction if inputs to the CR2032 are left unconnected.
The SRAM is controlled by the Petra MC2 sector, and the access time is
programmable. Refer to the description of the Petra MC2 emulation in the
MVME1X2P2 VME Embedded Controller Programmer’s Reference
Guide for more detail.
About the Battery
The power source for the onboard SRAM is a coin-type Panasonic
CR2032 device (or equivalent) with two lithium cells. The battery is
socketed for easy removal and replacement. Small capacitors are provided
so that the battery can be quickly replaced without data loss.
The service life of the battery is very dependent on the ambient
temperature of the board and the power-on duty cycle. The lithium battery
supplied on the MVME162P2 should provide at least two years of backup
time with the board powered off and with an ambient temperature of 40
°
C. If the power-on duty cycle is 50% (the board is powered on half of the
time), the battery lifetime is four years. At lower ambient temperatures, the
backup time is correspondingly longer.