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Data Sheet

The Rx5C338A are CMOS real-time clock ICs connected to the CPU by three signal lines CE (Chip Enable), SCLK (Serial Clock), and SIO (Serial Input/Output), and configured to perform serial transmission of time and calendar data to the CPU. These models incorporate different functional circuits. The periodic interrupt circuit is configured to generate interrupt signals with six selectable interrupts ranging from 0.5 seconds to 1 month. The 2 alarm circuits generate interrupt signals at preset times. The oscillation circuit is driven under constant voltage so that fluctuations in oscillation frequency due to voltage are small and supply current is also small (TYP. 0.35µA at 3 volts). The oscillation halt sensing circuit can be used to judge the validity of internal data in such events as power-on. The supply voltage monitoring circuit is configured to record a drop in supply voltage below two selectable supply voltage monitoring threshold settings. The 32-kHz clock output function is intended to output sub-clock pulses for the external microcomputer. The oscillation adjustment circuit is intended to adjust time counts with high precision by correcting deviations in the oscillation frequency of the crystal oscillator. These models come in an ultra-compact 10-pin SSOP (RS5C338A with a height of 1.25mm and a pin pitch of 0.5mm)and 10-pin SSOP-G (RV5C338A with a height of 1.2mm and a pin pitch of 0.5mm).


Timekeeping supply voltage ranging from 1.45 to 5.5 volts
Low supply current TYP. 0.35µA (MAX. 0.8µA) at 3 volts (at 25°C)
Only three signal lines (SCLK, SIO, and CE) required for connection to the CPU. Maximum clock frequency of 2 MHz (with VDD of 5 volts)
Time counters (counting hours, minutes, and seconds) and calendar counters (counting years, months, days, and weeks) (in BCD format)
1900/2000 identification bit for Year 2000 compliance
Interrupt circuit configured to generate interrupt signals (with interrupts ranging from 0.5 seconds to 1 month) to the CPU and provided with an interrupt flag and an interrupt halt circuit
2 alarm circuits (Alarm_W for week, hour, and minute alarm settings and Alarm_D for hour and minute alarm settings)
32-kHz clock circuit (CMOS output, equipped with a control pin)
Oscillation halt sensing circuit which can be used to judge the validity of internal data
Supply voltage monitoring circuit with two supply voltage monitoring threshold settings
Automatic identification of leap years up to the year 2099
Selectable 12-hour and 24-hour mode settings
Built-in oscillation stabilization capacitors (CG and CD)
High precision oscillation adjustment circuit
CMOS process
Ultra-compact 10-pin SSOP (RS5C338A with a height of 1.25mm and size of 6.4×3.5mm) Ultra-compact 10-pin SSOP-G (RV5C338A with a height of 1.20mm and size of 4.0×2.9mm)


  • Communication devices(multi function phone, portable phone, PHS or pager)
  • OA devices(fax, portable fax)
  • Computer(desk-top and mobile PC, portable word-processor, PDA, electric note or video game)
  • AV components (portable audio unit, video camera, camera, digital camera or remote controller)
  • Home appliances(rice cooker, electric oven)
  • Other(car navigation system, multi-function watch)

Documents Download

Data Sheet Package Info. Mark Info. Quality Assurance Data
Rx5C338A SSOP-10 to be prepared Reliability
SSOP-10G to be prepared Reliability

All PDF files are less than 1MB unless otherwise stated.

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