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DS1302 датащи(PDF) 5 Page - Maxim Integrated Products |
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DS1302 датащи(HTML) 5 Page - Maxim Integrated Products |
5 / 13 page DS1302 Trickle-Charge Timekeeping Chip 5 of 13 OSCILLATOR CIRCUIT The DS1302 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or capacitors to operate. Table 1 specifies several crystal parameters for the external crystal. Figure 1 shows a functional schematic of the oscillator circuit. If using a crystal with the specified characteristics, the startup time is usually less than one second. CLOCK ACCURACY The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional error will be added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the oscillator circuit may result in the clock running fast. Figure 2 shows a typical PC board layout for isolating the crystal and oscillator from noise. Refer to Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for detailed information. Table 1. Crystal Specifications* PARAMETER SYMBOL MIN TYP MAX UNITS Nominal Frequency fO 32.768 kHz Series Resistance ESR 45 k Ω Load Capacitance CL 6 pF *The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications. Figure 2. Typical PC Board Layout for Crystal LOCAL GROUND PLANE (LAYER 2) CRYSTAL X1 X2 GND NOTE: AVOID ROUTING SIGNALS IN THE CROSSHATCHED AREA (UPPER LEFT- HAND QUADRANT) OF THE PACKAGE UNLESS THERE IS A GROUND PLANE BETWEEN THE SIGNAL LINE AND THE PACKAGE. COMMAND BYTE Figure 3 shows the command byte. A command byte initiates each data transfer. The MSB (bit 7) must be a logic 1. If it is 0, writes to the DS1302 will be disabled. Bit 6 specifies clock/calendar data if logic 0 or RAM data if logic 1. Bits 1 to 5 specify the designated registers to be input or output, and the LSB (bit 0) specifies a write operation (input) if logic 0 or read operation (output) if logic 1. The command byte is always input starting with the LSB (bit 0). Figure 3. Address/Command Byte 1 RAM CK A4 A3 A2 A1 A0 RD WR 7654 3210 |
Аналогичный номер детали - DS1302 |
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Аналогичное описание - DS1302 |
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