Part Number: MCP79400-I/SN

Manufacturer: Microchip Technology


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Technical Specifications of MCP79400-I/SN

Datasheet  MCP79400-I/SN datasheet
Category Integrated Circuits (ICs)
Family Clock/Timing – Real Time Clocks
Manufacturer Microchip Technology
Packaging Tube
Part Status Active
Type Clock/Calendar
Features Alarm, Leap Year, Square Wave Output, SRAM, Unique ID
Memory Size 64B
Time Format HH:MM:SS (12/24 hr)
Date Format YY-MM-DD-dd
Interface I2C, 2-Wire Serial
Voltage – Supply 1.8 V ~ 5.5 V
Voltage – Supply, Battery 1.3 V ~ 5.5 V
Current – Timekeeping (Max) 1.2μA (Typ) @ 3.3V
Operating Temperature -40°C ~ 85°C
Mounting Type Surface Mount
Package / Case 8-SOIC (0.154″, 3.90mm Width)
Supplier Device Package 8-SOIC

MCP79400-I/SN Description

The MCP7940X RTCC is a real-time clock and calendar that keeps track of time with built-in hour, minute, second, day, month, and year counters. All time intervals, from seconds to months, can have alarms set. I2C communications at 400 kHz can be used for configuration and use with the MCP7940X. The open-drain, the versatile output, can assert on an alarm match, generate a square wave at a frequency of your choosing, or serve as a standard output.

Using external crystal load capacitors, the MCP7940X can run on a tuning fork crystal with a frequency of 32.768 kHz. To compensate for frequency variation due to crystal tolerance and temperature, on-chip digital trimming can be used. When the main power goes out, the backup supply keeps the device’s SRAM and timekeeping circuitry, so data can be reliably stored in both, even if the device is no longer running at the correct time. The power-fail timestamp records when the device begins using its backup power source and when the main power is restored. Ideal for storing a unique identifier or other crucial information, the MCP7940X’s 64 bits of EEPROM are only writable after an unlock sequence. EUI-48 addresses are built into the MCP79401, while EUI-64 lessons are built into the MCP79402. In addition, we offer programming tailored to your specific needs.

MCP79400-I/SN Features

Real-Time Clock/Calendar (RTCC)

– Hours, Minutes, Seconds, Day of Week, Day, Month, Year

– Leap year compensated to 2399

– 12/24-hour modes

Oscillator for 32.768 kHz Crystals:

– Optimized for 6-9 pF crystals

On-Chip Digital Trimming/Calibration:

– ±1 ppm resolution

– ±129 ppm

Power-Fail Timestamp:

– Time logged on the switchover to and from Battery mode


I2C Interface

The MCP7940X is equipped with a 2-wire bus and can communicate with various protocols. Transmitters and receivers send and receive data from the bus.

The MCP7940X is a slave device on the bus and must be controlled by a master device that provides the bus with start and stops conditions. The master device controls which mode is active so the slave device can either transmit or receive.

Functional Description

The MCP7940X is a Real-Time clock and calendar with extensive integration (RTCC). An internal, low-power oscillator keeps track of the current time in seconds, minutes, hours, days, dates, months, and years. Additional memory options on the MCP7940X include 64 bytes of general-purpose SRAM and 8 bytes of secure EEPROM. Two alarm modules can generate interruptions at predetermined times based on various comparison criteria.

It is possible to correct the crystal’s inherent imprecision using digital trimming. If primary power is lost, the MCP7940X will automatically switch to backup power via the backup supply input and an integrated power switch, keeping the current time and the contents of the SRAM intact throughout the transition. The clock module records the primary power outage and subsequent restoration. Every one of the MCP7940X’s modules can be accessed through the RTCC’s configuration and status registers.

● Oscillator Configuration

Depending on the application, the MCP7940X can function in either an external crystal oscillator configuration or an external clock input oscillator configuration.

● External Crystal

The crystal oscillator circuit on the MCP7940X is intended to function with a tuning fork crystal that operates at a standard frequency of 32.768 kHz and matching external load capacitors. Because it uses external load capacitors, the MCP7940X can accommodate a diverse range of crystals. Suitable crystals have a load capacitance (CL) value in the 6-9 pF. Using crystals with a load capacitance of 12.5 pF or higher is not suggested.

Considerations Regarding the Layout: The oscillator circuit should be installed on the side of the board that is parallel to the device. Position the oscillator circuit so that it is close to the oscillator pins. On the same side of the circuit board as the oscillator itself, the load capacitors should be positioned to be adjacent to the component.

Enclosing the oscillator circuit in a grounded copper pour will protect it from interference from other circuits. The copper pour that serves as ground must be connected directly to ground (VSS). Do not run any electrical or signal wiring inside the ground pour. In addition, if you’re using a board with two sides, keep the crystal away from the side where you plan to place traces.

● Timekeeping

The MCP7940X keeps track of the time and date using an external 32.768 kHz crystal or clock source. In these logbooks, you may keep track of the time down to the second, the duration of an event down to the hour, the day, the month, and the year.

The MCP7940X is programmed to make automatic adjustments for months with fewer than 31 days and to account for leap years beginning in 2001 and continuing until 2399. A number consisting of just two digits is used to store the year. There is support for both a 12-hour and 24-hour time format, and the 12/24 bit is used to select the design. The value of each day of the week counts from one to seven, with increments occurring at midnight; the representation is up to the individual user (i.e., the MCP7940X does not require 1 to equal Sunday, etc.). Binary-coded decimal (BCD) values are used to store all of the time and date information that is contained inside the registers.

Despite being powered by the backup source, the MCP7940X will not lose track of the current time or date it is displaying. When reading from the timekeeping registers, they are buffered so that errors caused by the rollover of counters are avoided. The following events are responsible for the updating of the buffers: • Whenever a read is requested from any of the RTCC registers (addresses 0x00 to 0x1F) • When performing a read operation on an RTCC register, when the registered address rolls over from 0x1F to 0x00

Reading all the timekeeping registers in a single operation will allow you to use the onboard buffers fully and keep rollover problems at bay.


The MCP7940X includes 64 bytes of general-purpose SRAM and eight bytes of secure EEPROM for storing data. If a secondary power source is turned on, the SRAM will remain functional even if the primary power source is cut. As a nonvolatile memory, EEPROM stores information even when power is cut. The SRAM and RTCC registers are in different blocks, although they share the same control byte (‘1101111X’). Given that the EEPROM is located in a separate address space, a unique control byte (‘1010111X’) is needed to access its data.

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