Technical data

4-8 Computer Group Literature Center Web Site
Functional Description
4
The SRAM is controlled by the MC2chip, and the access time is
programmable. Refer to the MC2chip description in the MVME172 VME
Embedded Controller Programmer’s Reference Guide for more detail.
About the Batteries
The power source for the onboard SRAM is an Electro Marketing EM1275
device (or equivalent, such as RAYOVAC FB1225) with two BR1225-
type lithium cells. The battery is socketed for easy removal and
replacement. Small capacitors are provided so that the batteries can be
quickly replaced without data loss.
The service life of the batteries is very dependent on the ambient
temperature of the board and the power-on duty cycle. The lithium
batteries supplied on the MVME172LX 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.
The MVME172LX is shipped with the batteries disconnected (i.e., with
VMEbus +5V standby voltage selected as both primary and secondary
power source). If you intend to use the battery as a power source, whether
primary or secondary, it is necessary to reconfigure the jumpers on J14
before installing the board. Refer to SRAM Backup Power Source Select
Header (J14) on page 1-9 for available jumper configurations.
The power leads from the battery are exposed on the solder side of the
board. The board should not be placed on a conductive surface or stored in
a conductive bag unless the battery is removed.