REV.-A
2.3.4.4 Memory Back-up Circuit
F?
The printer is equipped with SRAM
(IC6A)
that stores the printing mode, character pitch, and TOF (top “
--
of form) position set using the control panel. The memory back-up circuit is on the PEGX board so that
the settings can be maintained even when the printer power is turned off. A lithium battery is used to
back up the memory. Figure 2-32 shows the memory back-up circuit.
024
A1015
+5V
*
“
kc
ST-RAM
ZD8
:2:
HZS3 . ONBZ
HM6264 (6A)
R78
IK
MS
R77
150
R79
150
)77
J
CR
17335
Figure 2-32. Memory Back-up Circuit
When the power is turned on under normal conditions,
+5V
is applied to Vcc of the RAM and the CPU
starts reading and writing. When the power is turned off, and the voltage on the + 5V line decreases
to about
3.OV,
transistors Q24 and Q25 are switched off and the voltage from the external lithium
battery is applied to the
Vcc
terminal. The data in the static RAM is therefore maintained. Table 2-6
lists the static RAM conditions when the power is on or off.
Table 2-6. ST-RAM Conditions
Power
+5V
Line
CS2
Vcc [v]
ST-RAM mode
OFF
L
L
+3.0
-3.3 Data holding
ON
H
H
+5
Normal
<
.“
.-,
.
f“:
2-38
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