Epson LQ-860 Technical Manual page 80

2.3.1.4 ST-RAM (7A) Battery Backup Circuil
The ST-RAM (7A) employs a lithium battery (3.00 to 3.35 VDC) for backup, and is used to maintain the initial
data for the printer mechanism and settings for the control panel when the printer power is turned off.
Figure 2-28 shows the ST-RAM (7A) battery backup circuit, and Table 2-21 shows the ST-RAM conditions
when the power is turned on or off.
When the power is turned on under normal conditions, +5 V is applied to V~. of the ST-RAM, and the CPU
starts read/write operations. When the power is turned off, and the voltage on the +5 V line drops to about
3.3 V or less, transistors Q42 and Q43 turn off, and the voltage from the lithium battery (BTI) is applied to
the v~~ terminal of the ST-RAM. In this way, the data in the ST-RAM is maintained.
When the voltage from the lithium battery drclps, the initial data for the printer mechanism and settings for
the control panel are cleared, and default values are set at power is turned on.
Printer Power
OFF
J
R58
R59.
/
Figure 2-28. Battery Backup Circuit
Table 2-21. ST--RAM Conditions with Power On/Off
+5 V
Line
L
ON
H
(7A)
Vss
L 2.4- 2.7 Data holding
H + 5
2-33
ST-RAM Mode
Normal
I
REV.-A