Memory Back-Up Circuit - Ricoh FAX550 Service Manual

November 30th, 1991

1.6.2. Memory Back-up Circuit

+5V
Voltage
Detector
Reference:
Group 3
[A]
Facsimile
Manual,
section 1-4-3
(Circuit type 1)
+24V
5-1
[B]
Battery
The battery [A] on the MBU backs up the RAM on the MBU, which contains
system parameters. It also backs up the real time clock in the cpu. This bat-
tery is not rechargeable. CN1-9 tells the cpu whether the back-up power
(CN1-11) comes from the battery or from the + 5V supply.
A rechargeable battery [B] backs up the SAF memory and the real time clock
for 1 hour. When the main power is switched on, the + 24V supply charges
the battery. If there is data in the SAF, the battery also backs up the real time
clock, to preserve the MBU battery.
MBU
Switching
Circuit
+5V
Switching
Circuit
Regulator
5-2
1-12
OVERALL MACHINE INFORMATION
RAM
1-11 1-11
1-9 1-9
Battery
Switch
Real Time
Battery
POWER DISTRIBUTION
FCU
Clock
CPU
Memory
Monitor
SAF
Memory