1.6.2. Memory Back-up
The +5VBAT supply from the lithium battery [A] backs up the system RAM
which contains system parameters and programmed telephone numbers,
and the real time clock in the main CPU.
BRO China model:
Two dry cells [B] and the dc/dc converter on the FCU back up the DRAM, if
there is data in the SAF memory and the power is switched off.
The dry cells generate about 3 volts (max. 3.2 volts). The dc/dc converter
(IC30) lifts this voltage to 5 volts so it can be used as the +5VD supply for
SAF backup. The CPU monitors the voltage of the +5VD supply with the
VDVDET signal. When the dry cells have run down, and the voltage is lower
than 4.4 volts, the CPU stops the dc/dc converter by dropping 1SAFFG to low
and the machine stops backing up the memory.
There is no battery switch for the battery [B].
FCU
FCIP
Switching
Circuit
System
RAM
DRAM
POWERS
5RTCCS
+5VBAT
+5V
VDVDET
1SAFFG
Q3
+5V
DC/DC
Converter
[IC30]
+5V
+5V
+5V
+5VBAT
[A]
[B]
H068V502.wmf
OVERALL MACHINE INFORMATION August 7th, 1995
POWER DISTRIBUTION
1-14
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