Abstract: The DS1340-33 serial real-time clock (RTC) provides pin compatibility and is functionally (including software clock calibration) equivalent to the clock / calendar of ST Microelectronics M41T00, including software clock calibration.
Can be used directly as a replacement product without changing the PC board and software. In fact, DS1340-33 is an enhanced product, which has a lower time holding voltage (from 2.0V to 1.3V), the operating voltage of the 2-wire interface is reduced to 1.8V, the 2-wire bus speed is increased to 400kHz, and Can choose a smaller package. In addition, it can also provide trickle charging function on the VBACKUP pin, and has an oscillator termination flag bit, which requires two additional registers.
Package DS1340 provides two package options, the first is 8-pin SO package (150mil wide), the package is the same as M41T00M6, if DS1340 is used as the second source device, this package can be selected; the second is Smaller 8-pin µSOP package, the specific size of this package can be obtained through the following link: http://pdfserv.maxim-ic.com/arpdf/Packages/g2018_001.pdf. Electrical characteristics The following table gives the electrical characteristics of DS1340-33 and M41T00.
It can be clearly seen from the data in the table: DS1340-33 is superior to M41T00 in several aspects.
The power supply voltage range of DS1340-33 is small, but the -3 and -18 versions of DS1340 can be selected to obtain a lower operating voltage. In general, the DS1340 provides three operating voltage ranges: 1.71V to 1.89V, 2.7V to 3.3V and 2.97V to 5.5V.
One of the main advantages of the DS1340-33 is its wider backup supply voltage range. Even if the voltage drops to 1.3V, it can always keep the time valid. Adopt super capacitor and use internal trickle charger to charge, the backup power supply can be charged to the power supply voltage.
The DS1340-33 provides a fixed voltage switching threshold, which is the voltage at which the power supply switches between the power supply voltage and the backup power supply. The switching voltage of M41T00 depends on the backup power supply voltage.
When the 3.3V power supply is used and the temperature is + 25 ° C, the DS1340-33 and M41T00 maintain the same typical current value for a period of time. Dallas Semiconductor has verified that the DS1340-33's time hold current is less sensitive to voltage and temperature than the M41T00. Therefore, the use of DS1340-33 allows users to obtain a lower time to maintain current in the entire operating voltage and temperature range. The register map of DS1340 and M41T00 are the same, so there is no need to modify the firmware of the existing slot. Through two additional registers, a trickle charger and status bits (mask) can be provided. This is obviously designed for systems that do not use them.
Figure 1. Register map
For detailed information about each register, please refer to the DS1340 data sheet.
The data block access of the register is the same as the ST device. In the process of multi-byte access to the time holding register, if the address pointer reaches 07h, the RTC and control register addresses terminate and return to 00h.
The additional registers at addresses 08h and 09h are accessed by writing to the address pointer at the corresponding location. In the data block access mode, the address sequence is 08h, 09h, and then the address pointer returns to 00h. The sequence is the same as M41T00.
If writing firmware to any RTC, additional registers can be used to identify the device being used. M41T00 will confuse the address register setting with interval 8. In other words, register 0 can be accessed when the address is 0H, 8H, 10H, 18H ... DS1340-33 does not have this problem because it has unique registers at addresses 8H and 9H. At the end of this application note, a flow chart for identifying the RTC used is given. The 2-wire interface DS1340-33 supports the standard mode and fixed mode of the 2-wire interface, which means that the SCL clock frequency can reach 400kHz. M41T00 only supports standard mode, and its maximum frequency is 100kHz. Conclusion Through the above analysis, DS1340-33 can not only be used as the second source device of ST M41T00, but also has many improvements, including: the main power supply and backup power supply have a wider operating voltage range, a smaller package size, and faster Interface speed. In addition, it has an integrated trickle charger and oscillator stop flag.
RTC identification flow chart
Can be used directly as a replacement product without changing the PC board and software. In fact, DS1340-33 is an enhanced product, which has a lower time holding voltage (from 2.0V to 1.3V), the operating voltage of the 2-wire interface is reduced to 1.8V, the 2-wire bus speed is increased to 400kHz, and Can choose a smaller package. In addition, it can also provide trickle charging function on the VBACKUP pin, and has an oscillator termination flag bit, which requires two additional registers.
Package DS1340 provides two package options, the first is 8-pin SO package (150mil wide), the package is the same as M41T00M6, if DS1340 is used as the second source device, this package can be selected; the second is Smaller 8-pin µSOP package, the specific size of this package can be obtained through the following link: http://pdfserv.maxim-ic.com/arpdf/Packages/g2018_001.pdf. Electrical characteristics The following table gives the electrical characteristics of DS1340-33 and M41T00.
| Parameter | DS1340-33 | M41T00 | Units | ||||
| Min | Typ | Max | Min | Typ | Max | ||
| Supply Voltage | 2.97 | 3.3 | 5.5 | 2.0 | 5.5 | V | |
| Backup Supply Voltage | 1.3 | 5.5 | 2.0 | 3.0 | 3.5 | V | |
| Power-Fail Voltage | 2.70 | 2.8 | 2.97 | VBAT-0.70 | VBAT-0.50 | VBAT-0.20 | V |
| OperaTIng Current | 120 | 200 | 300 | µA | |||
| Standby Current | 85 | 125 | 70 | µA | |||
| TImekeeping Current, 2.97 to 5.5V, -40 ° C to + 85 ° C | 0.85 | 1.25 | Not specified | Not specified | µA | ||
| TImekeeping Current, 3.3V, + 25 ° C | 0.8 | 1.0 | 0.8 | 1.0 | µA | ||
It can be clearly seen from the data in the table: DS1340-33 is superior to M41T00 in several aspects.
The power supply voltage range of DS1340-33 is small, but the -3 and -18 versions of DS1340 can be selected to obtain a lower operating voltage. In general, the DS1340 provides three operating voltage ranges: 1.71V to 1.89V, 2.7V to 3.3V and 2.97V to 5.5V.
One of the main advantages of the DS1340-33 is its wider backup supply voltage range. Even if the voltage drops to 1.3V, it can always keep the time valid. Adopt super capacitor and use internal trickle charger to charge, the backup power supply can be charged to the power supply voltage.
The DS1340-33 provides a fixed voltage switching threshold, which is the voltage at which the power supply switches between the power supply voltage and the backup power supply. The switching voltage of M41T00 depends on the backup power supply voltage.
When the 3.3V power supply is used and the temperature is + 25 ° C, the DS1340-33 and M41T00 maintain the same typical current value for a period of time. Dallas Semiconductor has verified that the DS1340-33's time hold current is less sensitive to voltage and temperature than the M41T00. Therefore, the use of DS1340-33 allows users to obtain a lower time to maintain current in the entire operating voltage and temperature range. The register map of DS1340 and M41T00 are the same, so there is no need to modify the firmware of the existing slot. Through two additional registers, a trickle charger and status bits (mask) can be provided. This is obviously designed for systems that do not use them.
Figure 1. Register map
| Address | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 | FuncTIon | Range |
| 00H | EOSC | 10 Seconds | Seconds | Seconds | 00-59 | |||||
| 01H | R / W | 10 Minutes | Minutes | Minutes | 00-59 | |||||
| 02H | CEB | CB | 10 Hours | Hours | Century / Hours | 0-1; 00-23 | ||||
| 03H | R / W | R / W | R / W | R / W | R / W | Day | Day | 01-07 | ||
| 04H | R / W | R / W | 10 Date | Date | Date | 00-31 | ||||
| 05H | R / W | R / W | R / W | 10 Month | Month | Month | 01-12 | |||
| 06H | 10 Year | Year | Year | 00-99 | ||||||
| 07H | OUT | FT | S | CAL4 | CAL3 | CAL2 | CAL1 | CAL0 | Control | |
| 08H | TCS3 | TCS2 | TCS1 | TCS0 | DS1 | DS0 | ROUT1 | ROUT0 | Trickle Charger | |
| 09H | OSF | 0 | 0 | 0 | 0 | 0 | 0 | 0 | Flag | |
For detailed information about each register, please refer to the DS1340 data sheet.
The data block access of the register is the same as the ST device. In the process of multi-byte access to the time holding register, if the address pointer reaches 07h, the RTC and control register addresses terminate and return to 00h.
The additional registers at addresses 08h and 09h are accessed by writing to the address pointer at the corresponding location. In the data block access mode, the address sequence is 08h, 09h, and then the address pointer returns to 00h. The sequence is the same as M41T00.
If writing firmware to any RTC, additional registers can be used to identify the device being used. M41T00 will confuse the address register setting with interval 8. In other words, register 0 can be accessed when the address is 0H, 8H, 10H, 18H ... DS1340-33 does not have this problem because it has unique registers at addresses 8H and 9H. At the end of this application note, a flow chart for identifying the RTC used is given. The 2-wire interface DS1340-33 supports the standard mode and fixed mode of the 2-wire interface, which means that the SCL clock frequency can reach 400kHz. M41T00 only supports standard mode, and its maximum frequency is 100kHz. Conclusion Through the above analysis, DS1340-33 can not only be used as the second source device of ST M41T00, but also has many improvements, including: the main power supply and backup power supply have a wider operating voltage range, a smaller package size, and faster Interface speed. In addition, it has an integrated trickle charger and oscillator stop flag.
RTC identification flow chart
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