RTC-72421B

Real Time Clock Overview

The RTC-72421B is a 4-bit real-time clock module manufactured by Seiko Epson Corporation, housed in an 18-pin DIP package. It features a built-in crystal unit for adjustment-free operation and supports both 24-hour and 12-hour formats with automatic Gregorian leap year adjustment. The device operates within a temperature range of -10°C to +70°C and accepts a supply voltage (VDD) between 4.5 V and 5.5 V. Frequency precision is specified at ±50 × 10⁻⁶ at +25°C, with aging characteristics limited to ±5.0 × 10⁻⁶ per year.

Real Time Clock Feature Summary

• Built-in crystal unit eliminates the need for external oscillator components.
• Automatic leap year adjustment for the Gregorian calendar.
• Configurable 24-hour or 12-hour time format.
• Standard parallel interface with address/data multiplexing via ALE.

Real Time Clock Applications

• Car multimedia systems
• Body electronics
• Remote keyless entry units

Real Time Clock Procurement Notes

Verify the specific ordering suffix against the manufacturer's catalog to ensure correct frequency tolerance and environmental compliance. The part number RTC-72421B corresponds to the Q42724212000200 product code. Confirm that the application environment remains within the -10°C to +70°C operating temperature range specified for this variant.

Real Time Clock Selection Notes

Select the RTC-72421B when a parallel interface is required for system integration. Note that the 7242 series does not maintain complete compatibility with the older RTC-6242 series; technical differences must be reviewed during replacement planning. Ensure the host system provides the necessary control signals (/CS0, /RD, /WR, ALE) for proper data latching and register access.

Real Time Clock Part Context

This component belongs to the RTC-72421/72423 series of real-time clock modules. It is distinct from the RTC-72423, which utilizes a 24-pin SOP package. The 'B' designation indicates a frequency precision of ±50 ppm, differing from the 'A' variant which offers ±10 ppm precision. The module integrates counter logic for seconds, minutes, hours, days, months, and years.

Real Time Clock Replacement Considerations

Public confirmed substitute part numbers: None identified in verified documentation. The datasheet explicitly states that the 7242 series lacks complete compatibility with the legacy RTC-6242 series, requiring careful technical verification rather than direct pin-for-pin substitution.