Real-Time Clock/Nvram/Timer Function; About The Battery - Motorola MVME2700 Series Installation And Use Manual

Real-Time Clock/NVRAM/Timer Function

The MVME2700 employs an SGS-Thomson surface-mount M48T59
RAM and clock chip to provide 8KB of nonvolatile static RAM, a real-
time clock, and a watchdog timer function. This chip supplies a clock,
oscillator, crystal, power failure detection, memory write protection, 8KB
of NVRAM, and a battery in a package consisting of two parts:
The SNAPHAT battery package is mounted on top of the M48T559
device. The battery housing is keyed to prevent reverse insertion.
The clock furnishes seconds, minutes, hours, day, date, month, and year in
BCD 24-hour format. Corrections for 28-, 29- (leap year), and 30-day
months are made automatically. The clock generates no interrupts.
Although the M48T559 is an 8-bit device, 8-, 16-, and 32-bit accesses from
the ISA bus to the M48T559 are supported. Refer to the MVME2600/2700
Series Programmer's Reference Guide and to the M48T559 data sheet for
detailed programming and battery life information.

About the Battery

The power source for the real-time clock is an M4T28-BR12 SH1 lithium
battery which is socketed for easy removal and replacement.
The battery has a storage life of 50 years at 55° C. The length of its service
lifetime is very dependent on the ambient temperature of the board and the
power-on duty cycle. At 70° C, the anticipated time span for battery
protection (100% duty cycle) is 10 years. At lower ambient temperatures,
the backup time is correspondingly longer.
If you intend to place the board in storage, putting the M48T559 in power-
save mode by stopping the oscillator will extend the service life of the
battery. This is especially important at high ambient temperatures. To enter
power-save mode, execute the PPCBug PS command. Refer to
Commands on page 5-4
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A 28-pin 330mil SO device containing the real-time clock, the
oscillator, power failure detection circuitry, timer logic, 8KB of
static RAM, and gold-plated sockets for a battery
®
A SNAPHAT battery housing a crystal along with the battery
or its equivalent application-specific command.
Block Diagram
3
Debugger
3-13