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Feature-Rich, Low-Cost Timekeeping Solutions


A Real-Time Clock/Calendar (RTCC) maintains accurate time in an embedded system even when the main power is turned off.  Our RTCCs range from basic low-cost devices to highly integrated mid-range devices with either an I2C or SPI interface and include additional nonvolatile memory and a combination of features that are very useful when operating within a single battery-backed clock device. These cost-effective solutions offer more features and higher performance than many competitive devices and will meet the specific requirements of your application.

Why Choose Our RTCCs?


Innovative Peripherals

  • Battery switchover with power-fail timestamp
  • Wide digital trimming range
  • Watchdog timer with dual retriggers
  • Event detect inputs with a programmable debounce
  • Unique ID with a user unlock sequence

Easy to Implement

  • I2C and SPI interfaces
  • Industry-standard pinouts
    • I2C: 8 pins
    • SPI:  10 or 14 pins
  • RTCC-specific daughter boards that work with Microchip’s standard development platforms

Three Memory Options

  • Battery-backed SRAM
  • Nonvolatile EEPROM
  • Protected EEPROM area
    • Preprogrammed with unique EUI-48™ or EUI-64™ MAC address

Find The Right RTCC for Your Design


I2C RTCCs

Timing Features

  • Hours, minutes, seconds
  • Day of the week, day, month and year
  • Dual alarms: Single IRQ Out using VCC or VBAT
  • Programmable clock: 1 Hz to 32 kHz using VCC
  • Digital trimming from −127 ppm* to +127 ppm
    • Up to 11 seconds/day
  • Timestamp at battery switchover
    • VCC to VBAT
    • VBAT to VCC

*NOTE: 1 ppm ≈ 86 milliseconds/day

Memory Options

  • 64 bytes SRAM
  • 1 Kbits SEEPROM
  • 64 bits Unique ID
    • 0 = Blank
    • 1 = EUI-48 MAC address
    • 2 = EUI-64 MAC address

Voltage and Current

  • Main power (oscillator running)
  • VCC = 1.8V to 5.5V
  • ICC = < 5 μA
    • Battery backup (timekeeping and RAM)
      • VBAT = 1.3V to 5.5V
      • IBAT = < 700 nA

SPI RTCCs

Timing Features

  • Hours, minutes, seconds
    • Alarm down to 0.01 seconds
  • Day of the week, day, month and year
  • Dual alarms: Single IRQ Out using VCC or VBAT
  • Programmable clock out: 1 Hz to 32 kHz using VCC
  • 32 kHz boot clock at power up (MCP795BXX)
  • Digital trimming from −255 ppm* to +255 ppm
    • Up to 22 seconds/day
  • Timestamp at battery switchover
    • VCC to VBAT
    • VBAT to VCC
  • Watchdog timer
    • SPI retrigger
    • I/O retrigger

*NOTE: 1 ppm ≈ 86 milliseconds/day

Memory Options

  • 64 bytes SRAM
  • 2 Kbits or 1 Kbits EEPROM
  • 128 bits Unique ID
  • 0 = Blank
  • 1 = EUI-48 MAC address
  • 2 = EUI-64 MAC address

Voltage and Current

  • Main power (oscillator running)
    • VCC = 1.8V to 5.5V
    • ICC = < 1 μA
  • Battery backup (timekeeping and RAM)
    • VBAT = 1.3V to 5.5V
    • IBAT = < 700 nA

Get Started with These Development Tools


Use our Real-Time Clock PICtail™ daughter boards, along with a PICtail Plus Expansion Board and an Explorer 16/32 Development Board, to evaluate real-time clock functionality in microcontroller-based embedded applications.

MCP7941X PICtail Plus Daughter Board (I2C)

MCP795XX PICtail Plus Daughter Board (SPI)

PICtail Plus Expansion Board

Explorer 16/32 Development Board

How Can You Use an RTCC in Your Application?


While there are many ways that RTCC technology can be used to enhance an embedded design, here are a few examples of how an RTCC can be used:

  • Enable wired and wireless communications between devices in smart energy applications using an RTCC with a MAC address
  • Use digital trimming in the RTCC to perform software temperature compensation for more accurate timekeeping in utility metering applications
  • Provide any Ethernet application with its own unique identification using the RTCC’s EUI-48 or EUI-64 MAC address
  • Display the time of day and date on the LCD in any embedded system

Additional Clock and Timing Technologies


Whatever your complex timing requirements are, we offer a comprehensive portfolio of technologies, services, and solutions to help you build more reliable systems. Visit our Clock and Timing page to learn more about our atomic clocks, buffers, crystals, oscillators and other timing products.

Documentation

Title Download
TB3065-Enabling Intelligent Automation Using MCP7941X I2C RTCC Download
AN1364 - Using the Alarm Feature on the MCP79410 RTCC to Implement a Delayed Alarm Download
AN1413 - Temperature Compensation of a Tuning Fork Crystal Based on MCP79410 Download
AN1414 - Using HI-TECH C Compiler to Interface RTCC Devices to 8-Bit PIC MCUs Download
AN1365 - Recommended Usage of Microchip Serial RTCC Devices Download
AN1355 - A Complete Electronic Watch Based on MCP79410 I2C? RTCC Download
Title Download
I2C and SPI Real-Time Clock/Calendar Product Overview Download

What Is an RTCC?


Many electronic systems need to be able to tell time. Real Time Clocks (RTCs), also known as Real Time Clock/Calendars (RTCCs), are often the timekeepers for these electronic systems. While a system clock counts ticks to control the internal timing of a digital system, an RTCC tracks time in an hours/minutes/seconds format so the time information is relevant and comprehensible to humans. This makes an RTCC critical in many applications where providing a record of time is essential.

An RTCC works in conjunction with a precision oscillator, normally a crystal, which can be internal or external to the RTCC device. The RTCC counts the oscillations to keep track of the time and date. A communication interface is required to configure the device and set or fetch the time. RTCCs typically also have alarms which can be set to alert the system at specific times and dates.

How Does an RTCC Work?

An RTCC uses 32.768 kHz oscillations to provide a clock to the internal counters as shown in the figure on the right. A 15-bit counter overflows every 32,768 clocks (which is every second), providing a consistent time base. The counter feeds additional counters, which count the seconds, tens of seconds, minutes and so on, up to tens of years. If available, alarms compare the current values of the time counters to the alarm registers. If there is a match, the RTCC will modify a flag bit in an internal register or change the state of an output pin.

How Does the RTCC Begin Oscillation?

As noted above, an RTCC works with an oscillator, which is typically a quartz crystal that is shaped to vibrate at a specific frequency. Most RTCC devices use a 32.768 kHz quartz crystal, which is often referred to as a watch crystal. They also typically use an internal inverting amplifier circuit, as shown in the figure on the right, to resonate the crystal. The amplifier is configured with two feedback paths between its output and input that cause it to resonate or oscillate.

The oscillator circuit is not resonating before the RTCC's amplifier is enabled. When the amplifier is enabled, any thermal or background noise picked up by the oscillator circuit is amplified and causes the system to begin to oscillate. The oscillations quickly grow in amplitude.

The internal resistor (Rf) provides a non-frequency-specific feedback path around the amplifier. This assists in starting oscillations, but it has relatively high impedance. The crystal has much lower impedance at the rated frequency and rapidly dominates over the internal resistor to set the frequency of the oscillations. Capacitors (C1 and C2) ensure stable oscillation. Their values are determined by the crystal used and any other capacitance in the oscillator circuit.

How Does Temperature Affect Timekeeping?

Crystals only resonate at their rated frequency at a specified temperature. This is typically 25°C for 32.768 kHz tuning-fork watch crystals. The crystal will resonate at lower frequencies at other temperatures. This is a highly predictable property of the thermal expansion of quartz. While minor changes in temperature may not be an issue, as temperatures move further away from 25°C, the variance in frequency may cause the RTCC to lose significant amounts of time. Therefore, many RTCC devices offer a digital trimming or analog compensation scheme that can adjust for the frequency error to ensure accurate timekeeping.

When Would You Use an RTCC?


An RTCC can be used any time your system needs to keep a track of time. You could use the counter/timer in a microcontroller, but an RTCC offers some key benefits. It provides battery backup so the time is not lost when the system loses power. A processor can offload time and alarm handling to an RTCC to avoid the periodic software time updates and comparisons required with alarms. The power difference between being in an idle, low-power standby mode and actively executing instructions can be substantial in a processor. Using an RTCC to handle timekeeping and to wake the processor on alarms or other events can lower the overall system power consumption.

What is Battery Backup?


Without battery backup, an RTCC's recorded time would reset when the system loses power. Battery backup allows the RTCC to switch to an alternate power source when system power is not available. This alternate power source manages the timekeeping counters, oscillator circuitry and alarm circuits, allowing the RTCC to continue to operate during a power loss. To reduce power consumption and enable longer operation, the communications portion of the RTCC is disabled when operating from the alternate power source. Because of their low cost, widespread availability and convenient cell voltage, lithium coin cell batteries are often used as the alternate power source for RTCCs.

What is BCD?


Binary Coded Decimal (BCD) is used with displays or other system interactions with the real world. To show the time and control a display, the system must break decimal numbers down into the individual ones, tens, hundreds and thousands digits. RTCCs record time in BCD to simplify handling and user-interfacing code. These decimal values are shown below and decomposed into BCD where four bits represent each digit.

Decimal Hex BCD* Thousands BCD* Hundreds BCD* Tens BCD* Ones
0 0x00 0000 0000 0000 0000
1 0x01 0000 0000 0000 0001
10 0x0A 0000 0000 0001 0000
255 0xFF 0000 0010 0101 0101

*Binary Coded Decimal

Real-Time Clock Products

View All Parametrics
Product Status 5K Pricing Automotive Capable Pin Count Interface Max Interface Speed Vcc Range (V) Vbat Range (V) Ibat Current (nA) Power-Fail Timestamp User SRAM (Bytes) EEPROM (Kbits) Unique ID (MAC_Address) Unique_ID (Bits) Alarms Outputs Minimum Clock_Count Digital_Trimming Temperature Range Packages
MCP79401 In Production $0.72 Yes 8 I²C™ 400 KHz 1.8 - 5.5 1.3 - 5.5 700 VCC Fail and VCC Restore 64 0 EUI-48 64 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +85 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC
MCP79402 In Production $0.72 Yes 8 I²C™ 400 KHz 1.8 - 5.5 1.3 - 5.5 700 VCC Fail and VCC Restore 64 0 EUI-64 64 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +85 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC
MCP7940M In Production $0.46 Yes 8 I²C™ 400 KHz 1.8 - 5.5 64 0 None 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +85 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC, 8/PDIP
MCP7940N In Production $0.59 Yes 8 I²C™ 400 kHz 1.8 - 5.5 1.3 - 5.5 700 VCC Fail and VCC Restore 64 0 None 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +125 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC, 8/PDIP
MCP79410 In Production $0.72 Yes 8 I²C™ 400 KHz 1.8 - 5.5 1.3 - 5.5 700 VCC Fail and VCC Restore 64 1 Blank ID 64 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +85 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC
MCP79411 In Production $0.78 Yes 8 I²C™ 400 KHz 1.8 - 5.5 1.3 - 5.5 700 Vcc Fail and Vcc Restore 64 1 EUI-48 64 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +85 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC
MCP79412 In Production $0.78 Yes 8 I²C™ 400 KHz 1.8 - 5.5 1.3 - 5.5 700 Vcc Fail and Vcc Restore 64 1 EUI-64 64 2 Alarms (1 sec) IRQ/CLK 1 sec -127 to +127ppm (1 ppm steps) -40 to +85 8/MSOP, 8/TDFN, 8/TSSOP, 8/SOIC

NOTE: Battery switchover with power-fail timestamp and digital trimming in all RTCCs unless noted.

View All Parametrics
Product Status 5K Pricing Automotive Capable Pin Count Interface Max Interface Speed Vcc Range (V) Vbat Range (V) Ibat Current (nA) Power-Fail Timestamp User SRAM (Bytes) EEPROM (Kbits) Unique ID (MAC_Address) Unique_ID (Bits) Alarms Outputs Minimum Clock_Count Digital_Trimming Watchdog Timer Event Detects 32KHz Boot Clock Temperature Range Packages
MCP79510 In Production $0.90 Yes 10 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 1 Blank 128 2 Alarms (0.01sec) IRQ/CLK 0.01 sec -255 to +255ppm (1 ppm steps) NO 0 NO -40 to +85 10/MSOP, 10/TDFN
MCP79511 In Production $0.96 Yes 10 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 1 EUI-48 128 2 Alarms (0.01sec) IRQ/CLK 0.01 sec -255 to +255ppm (1 ppm steps) NO 0 NO -40 to +85 10/MSOP, 10/TDFN
MCP79512 In Production $0.96 Yes 10 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 1 EUI-64 128 2 Alarms (0.01sec) IRQ/CLK 0.01 sec -255 to +255ppm (1 ppm steps) NO 0 NO -40 to +85 10/MSOP, 10/TDFN
MCP79520 In Production $0.96 Yes 10 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 2 Blank 128 2 Alarms (0.01sec) IRQ/CLK 0.01 sec -255 to +255ppm (1 ppm steps) NO 0 NO -40 to +85 10/MSOP, 10/TDFN
MCP79521 In Production $1.02 Yes 10 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 2 EUI-48 128 2 Alarms (0.01sec) IRQ/CLK 0.01 sec -255 to +255ppm (1 ppm steps) NO 0 NO -40 to +85 10/MSOP, 10/TDFN
MCP79522 In Production $1.02 Yes 10 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 2 EUI-64 128 2 Alarms (0.01sec) IRQ/CLK 0.01 sec -255 to +255ppm (1 ppm steps) NO 0 NO -40 to +85 10/MSOP, 10/TDFN
MCP795W10 In Production $1.22 Yes 14 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 1 Blank 128 2 Alarms (0.01sec) IRQ WDO CLKOUT 0.01 sec -255 to +255ppm (1 ppm steps) Yes 2 NO -40 to +85 14/TSSOP, 14/SOIC
MCP795W11 In Production $1.28 Yes 14 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 1 EUI-48 128 2 Alarms (0.01sec) IRQ WDO CLKOUT 0.01 sec -255 to +255ppm (1 ppm steps) Yes 2 NO -40 to +85 14/TSSOP, 14/SOIC
MCP795W12 In Production $1.28 Yes 14 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 1 EUI-64 128 2 Alarms (0.01sec) IRQ WDO CLKOUT 0.01 sec -255 to +255ppm (1 ppm steps) Yes 2 NO -40 to +85 14/TSSOP, 14/SOIC
MCP795W20 In Production $1.28 Yes 14 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 2 Blank 128 2 Alarms (0.01sec) IRQ WDO CLKOUT 0.01 sec -255 to +255ppm (1 ppm steps) Yes 2 NO -40 to +85 14/TSSOP, 14/SOIC
MCP795W21 In Production $1.34 Yes 14 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 2 EUI-48 128 2 Alarms (0.01sec) IRQ WDO CLKOUT 0.01 sec -255 to +255ppm (1 ppm steps) Yes 2 No -40 to +85 14/TSSOP, 14/SOIC
MCP795W22 In Production $1.34 Yes 14 SPI 10 MHz 1.8 - 3.6 1.3 - 3.6 700 VCC Fail and VCC Restore 64 2 EUI-64 128 2 Alarms (0.01sec) IRQ WDO CLKOUT 0.01 sec -255 to +255ppm (1 ppm steps) Yes 2 NO -40 to +85 14/TSSOP, 14/SOIC

8-bit USB PIC Microcontrollers with Active Clock Tuning

Microchip Technology expands its Full-Speed USB 2.0 Device PIC® microcontroller portfolio with three new Enhanced Midrange 8-bit families comprising 15 scalable MCUs ranging from 14 to 100 pins with up to 128 KB of Flash.  All feature internal clock sources with the 0.25% clock accuracy necessary for USB communication, which saves up to $0.15 by eliminating the need for an external crystal.  Additionally, all three families are eXtreme Low Power compliant, with power consumption down to 35 µA/MHz Active and 20 nA in Sleep mode.