This post explains for the voltage detector.
The Part Number is KIA7042AP.
The function of this semiconductor is 4.2V, Voltage detector.
Preview images :
Function of this IC is accurately resetting the system after detecting voltage at the time of switching power on and instantaneous power off in various CPU systems and other logic systems.
1. Current Consumption is Low. ICCL=300 A Typ. ICCH=30 A Typ.
2. Resetting Output Minimum Guarantee Voltage is Low 0.8V Typ.
3. Hysteresis Voltage is Provided. 50mV Typ […]
1. As Control Circuit of Battery-Backed Memory.
2. As Measure Against Erroneous Operations at Power ON-OFF.
3. As Measure Against System Runaway at Instantaneous Break of Power Supply etc.
4. As Resetting Function for the CPU-Mounted Equipment, such as Personal Computers, Printers, VTRs and so forth