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DS1747-70IND+ Datasheet(PDF) 5 Page - Maxim Integrated Products |
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DS1747-70IND+ Datasheet(HTML) 5 Page - Maxim Integrated Products |
5 / 16 page DS1747/DS1747P Y2K-Compliant, Nonvolatile Timekeeping RAMs 5 of 16 Table 1. Truth Table VCC CE OE WE MODE DQ POWER VIH X X Deselect High-Z Standby VIL X VIL Write Data In Active VIL VIL VIH Read Data Out Active VCC>VPF VIL VIH VIH Read High-Z Active VSO<VCC<VPF X X X Deselect High-Z CMOS Standby VCC<VSO<VPF X X X Deselect High-Z Data-Retention Mode SETTING THE CLOCK As shown in Table 2, bit 7 of the century register is the write bit. Setting the write bit to a one, like the read bit, halts updates to the DS1747 registers. The user can then load them with the correct day, date and time data in 24-hour format. Resetting the write bit to a zero then transfers those values to the actual clock counters and allows normal operation to resume. STOPPING AND STARTING THE CLOCK OSCILLATOR The clock oscillator may be stopped at any time. To increase the shelf life, the oscillator can be turned off to minimize current drain from the battery. The OSC bit is the MSB (bit 7) of the seconds registers, see Table 2. Setting it to a one stops the oscillator. FREQUENCY TEST BIT As shown in Table 2, bit 6 of the day byte is the frequency test bit. When the frequency test bit is set to logic “1” and the oscillator is running, the LSB of the seconds register will toggle at 512Hz. When the seconds register is being read, the DQ0 line will toggle at the 512Hz frequency as long as conditions for access remain valid (i.e., CE low, OE low, WE high, and address for seconds register remain valid and stable). CLOCK ACCURACY (DIP MODULE) The DS1747 is guaranteed to keep time accuracy to within 1 minute per month at +25C. The RTC is calibrated at the factory by Maxim using nonvolatile tuning elements, and does not require additional calibration. For this reason, methods of field clock calibration are not available and not necessary. The electrical environment also affects the clock accuracy, and caution should be taken to place the RTC in the lowest-level EMI section of the PC board layout. For additional information, refer to Application Note 58. CLOCK ACCURACY (PowerCap MODULE) The DS1747 and DS9034PCX are each individually tested for accuracy. Once mounted together, the module typically keeps time accuracy to within 1.53 minutes per month (35 ppm) at +25°C. Clock accuracy is also affected by the electrical environment and caution should be taken to place the RTC in the lowest-level EMI section of the PC board layout. For additional information, refer to Application Note 58. |
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