M41T00SM6F is a Serial Real-Time Clock for Time-Specific Devices

You know that popular saying of “early to bed; early to rise.” It simply means that when you get to bed (sleep) early, there is probably a higher chance that you would wake up earlier too. The same applies to consumer electronics – when these devices use an accurate timekeeping component, there is the chance that the functions wouldn’t be interrupted.

Speaking of a timekeeping component, the Real-Time Clock (RTC) makes all the difference. We are happy to review M41T00SM6F, one of the best RTCs out there.

M41T00SM6F as a Serial Real-Time Clock

Before we talked about the “seriality” of the M41T00SM6F, let us first understand what a Real-Time Clock (RTC) is all about.

A Real-Time Clock or “RTC” is a dedicated electronic device or component, often designed as an Integrated Circuit (IC). It is to be added or attached as a carry-on device on embedded systems. The function is to provide accurate timekeeping for the embedded systems, with a particular emphasis on electronic devices.

For the RTC to function perfectly, it needs to keep an updated time and what could be a better way than having constant power supplied to it? That is why most RTCs now have several power sources, ranging from the rechargeable batteries and supercapacitors.

In terms of serial Real-Time Clocks like M41T00SM6F, the function is to ensure that the operations of the electronics or embedded systems don’t stop. For that purpose, STMicroelectronics, M41T00SM6F’s manufacturer released a range of serial RTCs to fill that void.

These set of serial RTCs are designed to provide low-power serial clocking. The RTCs are also configured or optimized with the Binary Coded Decimal (BCD) and could maintain full-power using the externally-controlled, built-in 32.768 kHz oscillator.

Powering Sources for the M41T00SM6F

M41T00SM6F is one of the many Serial RTCs by STMicroelectronics. It uses the same power source as the other RTCs – which is a combination of battery and crystal option.

For the battery operation, it relies on the replaceable and removeable SNAPHAT battery top. It is a dedicated battery used for powering the clock. It contains both a lithium coin-cell battery and a 32-kHz crystal oscillator.

The dual-battery architecture allows the M41T00SM6F and indeed, all other STMicroelectronic’s RTCs to keep clocking perfectly even when the main power source is off.

Besides, the SNAPHAT battery is optimized in a way that it doesn’t interfere with the overall performance of the circuit board. Ideally, it is only mounted or placed atop the circuit board after the System-on-a-Chip (SOIC) has been mounted on the PC board. That way, the SNAPHAT battery and the 32-kHz crystal oscillator wouldn’t be overly exposed to the higher temperatures obtainable during the Surface-mount processes.

Excellent Clocking Performance through Data Transitioning

Besides ensuring that the time is accurate, another function of a serial Real-Time Clock is to transmit data. In the case of M41T00SM6F, we have found out that it has an excellent clocking performance that combines with the data processing.

The procedure involves the 8-byte register map, which includes the following:

  • Calibration register
  • Seconds register
  • Year register
  • Minutes register
  • Date register
  • Day register
  • Month register
  • Century and hours register

Now, these 8 registers making up the 8-bytes tend to positively influence the data transmission process in the following ways:

1. Clock Data Reading

The 8-bytes of registers are used to set both the clock and the time and the date from the register. This is done with the Binary Coded Decimal (BCD) format and in such an instance, the trio of hours, seconds and minutes are prioritized for reading in the registers.

Now that we have ascertained the registers to be read, let us look at the data transmission process. For data to be passed across using the clock, it has to be done when the clock register updates are halted. The reason is that when the registers are being updated, the transition of data during the READ process might be negatively impacted.

2. Inter-IC Communications

M41T00SM6F also supports inter-communication among or between the supported Integrated Circuits (ICs). The best way to go about this is by leveraging the 2-wire bus, which is intended for use with the IC’s communications.

The 2-wire bus comprises both the Clock Signal (SCL) and the Bidirectional Data Signal (SDA). These two signal lines are to be used to bolster IC communication via the connection to a positive supply. A pull-up resistor is required to make this connection.

M41T00SM6F’s Clock Calibration

Besides the performance of the signals and data transmission process; another important factor to consider is the clock calibration. If the clock doesn’t calibrate properly, there is a chance that it wouldn’t performance optimally.

Here are the core clock calibration properties of the M41T00SM6F Serial Real-Time Clock:

3. Improved Accuracy

One of the benefits of the calibration is that the clocking performance or accuracy will improve. For the improvement to be made, M41T00SM6F’s clock calibrator needs to be driven by the quartz-controlled oscillator – which uses a nominal frequency of 32,768 Hz.

The target devices are also subjected to a test to ensure that they don’t exceed ±35 ppm (Parts Per Million). This rating is also expected to align with the oscillator frequency error at 25˚C. The error is also required to equate to about ±1.53 minutes every month.

4. Oscillation Rate

The other aspect of M41T00SM6F’s clock calibration improvement is when the oscillation rate of the crystals changes or improve with the temperature.

For accurate timing, a periodic counter correction is used to check for these changes. The idea is that a subtraction of counts tends to slow the clock down. However, when the temperature changes and the oscillation rate changes with it to the upside, there is a chance that the clocks will speed up – provided that the counts are added.

M41T00SM6F Product Attributes

Below are some of the properties making up the M41T00SM6F Serial Real-Time Clock:

Supported Interfaces2-wire Serial Bus and I2C Interfaces.
Operating TemperatureBetween -40˚C and 85˚C
Date FormatYY-MM-DD-dd
Time FormatHH:MM:SS (24-hour)


M41T00SM6F is a reliable Serial Real-Time Clock designed to speed up the clocking performances of surface-mount devices, automatically updates the different clock registers and detect power failures.