Rtc (Real Time Clock)/ Reset/ Eeprom Circuit - Epson PH890 Service Manual

EPSON Stylus Photo 890/1290

2.2.2.2 RTC (Real Time Clock)/ Reset/ EEPROM Circuit

RTC9822**includes built-in RTC and EEPROM and functions as a reset. The RTC
part has an electric two-layer condenser for backup. The RTC/Reset/EEPROM circuits
are attached on the C393MAIN board to monitor two voltages: +5V for the logic line
and +42V for the drive line. When each circuit detects abnormality on the
corresponding line, it resets CPU and ASIC to prevent the printer from operating
abnormally.
IC4 RTC9822** is attached on the main board as a RTC/Reset/ EEPROM circuit IC.
EEPROM part backups default setting value and each parameter. IC4
RTC9822**monitors +3.3, +5V, and +45 lines but can reset them independently. See
Figure 2-17 for the block diagram for the reset circuits.
Figure 2-17. RTC/Reset/EEPROM Circuit Block Diagram
o
+3.3V Line Reset Circuit
The VDD port of IC4 reset IC monitors the +5V line. When the IC detects an
abnormal voltage level (2.5 V or lower), it outputs a reset signal from the RST port
to CPU and ASIC.
o
+5V Line Reset Circuit
The VDD port of IC4 reset IC monitors the +5V line. When the IC detects an
abnormal voltage level (4.2 V or lower), it outputs a reset signal from the RST port
to CPU and ASIC.
OPERATING PRINCIPLES
o
+42V line reset circuit
The VIN port of the IC5 reset IC monitors the +45V line. When the IC detects an
abnormal voltage level (36V or lower), it outputs a reset signal from the VDT port
to CPU and ASIC.
Electrical Circuit Operating Principles
Revision B
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