2. DRAM Backup
While the machine is switched on, the +5VD supply, which comes from the
+5V signal, supplies the DRAM.
In energy saver mode level 2, the energy saver cpu will disable the +5V sup-
ply if there is no data in the DRAM. However, if there is data in the DRAM,
the +5V supply will not be disabled, and +5VD will continue to supply the
DRAM. If the machine has a hard disk, the +5V supply will only be killed if
there are no received fax messages or fax messages for transmission on the
disk.
While the machine is turned off, the rechargeable battery ([D] BAT1 on the
MFDU) supplies the SAF memory. It can back up the DRAM for an hour.
The battery [D] generates about 3 volts (max. 3.2 volts). The dc/dc converter
pumps up this voltage to 5 volts so it can be used for DRAM backup. The
CPU monitors the voltage of the +5VD supply with the 1VDET signal. When
the battery has run down to 4.4 volts, the CPU stops the dc/dc converter by
dropping 1SAFFG to low to stop DRAM backup.
Note that recharging the battery [D] takes one or two days after it has been
discharged.
Cross-reference
Energy Saver Modes: Section 2.3.1
December 21st, 1995
OVERALL MACHINE INFORMATION
POWER DISTRIBUTION
1-25
