The MCP79400 is a low-power I²C RTCC that tracks seconds, minutes, hours, day-of-week, date, month, and year, with leap-year compensation up to year 2399 and selectable 12/24-hour formats. It is designed for embedded systems that require reliable real-time clock functionality and event logging.

The device features automatic switchover to battery backup. When the primary supply is removed and a backup source is present, timekeeping and SRAM contents are preserved, and the transition events are recorded using a power-fail timestamp. The on-chip protected EEPROM (8 bytes) requires a specific unlock sequence, helping safeguard critical data.

Variant note: MCP79400 provides an unprogrammed protected EEPROM. MCP79401 and MCP79402 variants include factory-programmed EUI-48™ and EUI-64™ identifiers respectively.

MCP79400-I/SN denotes the Industrial temperature grade supplied in an SN package, which is an 8-lead SOIC (3.90 mm body) surface-mount package. Always verify land pattern and mechanical dimensions using the official Microchip package drawing.

The SOIC-8 pinout integrates crystal connections, I²C interface pins, a backup supply input, and a multifunction output for alarm or clock signaling.

• X1 / X2: 32.768 kHz crystal connections
• VBAT: Backup battery supply input (1.3V - 5.5V)
• VSS: Ground reference
• VCC: Main power supply (1.8V - 5.5V)
• MFP: Multifunction open-drain output (alarm/square wave/GPIO)
• SCL: I²C serial clock input (400kHz max)
• SDA: I²C serial data (bidirectional)

Devices within the MCP7940X family share the same electrical and pin-compatible design, with differences primarily in EEPROM programming.

• MCP79401-I/SN - Same family; factory-programmed EUI-48™ identifier
• MCP79402-I/SN - Same family; factory-programmed EUI-64™ identifier
• DS1307ZN+ - Basic I²C RTC (verify feature set and voltage compatibility)
• PCF8563T/F4,112 - Low-power I²C RTC (confirm register behavior and backup scheme)
• RV-8803-C7 - High-accuracy TC RTC (±1 ppm, no SRAM/EEPROM)

Note: Always verify register map, timing behavior, and PCB footprint before approving substitutes in production designs.

Microchip Technology Inc. (NASDAQ: MCHP) is a leading provider of smart, connected, and secure embedded control solutions. Founded in 1989 and headquartered in Chandler, Arizona, Microchip serves more than 100,000 customers across industrial, automotive, consumer, aerospace, and defense markets.

The MCP7940X family delivers low-power real-time clock functionality with integrated memory for embedded systems. Microchip maintains extensive design resources including application notes, reference designs, and the MPLAB® development ecosystem.

Quick Start Checklist

// Initialize MCP79400
Wire.beginTransmission(0x6F);  // I2C address
Wire.write(0x00);               // Start at seconds register
Wire.write(0x80);               // Start oscillator (ST bit)
Wire.endTransmission();

// Set time: 12:30:00
Wire.beginTransmission(0x6F);
Wire.write(0x00);
Wire.write(0x00);  // Seconds
Wire.write(0x30);  // Minutes
Wire.write(0x12);  // Hours (12-hour format)
Wire.endTransmission();