Functional Description
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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 present on the MVME172P4. 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
MVME1X2P4 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 MVME172P4 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.
If you intend to place the board in storage, putting the M48T58 in power-
save mode by stopping the oscillator will prolong battery life. This is
especially important at high ambient temperatures. To enter power-saving
mode, execute the 172Bug PS command (refer to Debugger Commands in
Chapter 3) or its equivalent application-specific command. When restoring
the board to service, execute the 172Bug SET command (set
mmddyyhhmm) after installation to restart the oscillator and initialize the
clock.
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