Sony IT-M708 Operation Manual page 25

Power cut detection and backup
When the unit operate by batteries, the unit detect Power cut by POWER DOWN Port in CPU and
keeps telephone conversation for 30 minutes (in case of new batteries being used)
Power cut detection
Power source is observed at DC jack input, and if this power goes down under 7V, Power cut is
noticed to CPU.
If CPU detects "L" on this POWER DOWN port,
1. Ports not relating to EEPROM become to Hi-Z (high impedance).
2. Data is evacuated into EEPROM.
3. Wait for a period which data is written into EEPROM (approximately 10ms).
4. CPU clock shift to SUB CLK (32.768KHz), and only clock count operation is made to reduce
power consumption.
5. During this time, POWER DOWN port is observed and if Power source recover, RESTART is
set by S/W (software).
6. When the power cut is still not recovered, when CPU power becomes under 3.5V, RESET
port
of CPU shift to LOW and operation of CPU stop.
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