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DS1685Q-3 Datasheet(PDF) 5 Page - Dallas Semiconductor |
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DS1685Q-3 Datasheet(HTML) 5 Page - Dallas Semiconductor |
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5 / 39 page  DS1685/DS1687 3V/5V Real-Time Clocks 5 of 39 PIN DESCRIPTIONS PIN DS1685 DS1687 DIP, SO, TSSOP PLCC EDIP NAME FUNCTION 1 2 1 PWR Active Low Power-On Output, Open Drain. The PWR pin is intended for use as an on/off control for the system power. With VCC voltage removed from the DS1685/DS1687, PWR can be automatically activated from a kickstart input by the KS pin or from a wake-up interrupt. Once the system is powered on, the state of PWR can be controlled by bits in the Dallas registers. The PWR pin can be connected through a pullup resistor to a positive supply. The voltage of the pullup supply should be no greater than 5.5V. — 1, 11, 13, 18 2, 3, 16, 20 N.C. No Connection. Pins missing by design. 2 3 — X1 3 4 — X2 Connections for Standard 32.768kHz Quartz Crystal. For greatest accuracy, the DS1685 must be used with a crystal that has a specified load capacitance of either 6pF or 12.5pF. The crystal-select ( CS) bit in Extended Control Register 4B is used to select operation with a 6pF or 12.5pF crystal. The crystal is attached directly to the X1 and X2 pins. There is no need for external capacitors or resistors. Note: X1 and X2 are very high- impedance nodes. It is recommended that they and the crystal be guard- ringed with ground and that high-frequency signals be kept away from the crystal area. 4–11 5–10, 12, 14 4–11 AD0–AD7 Multiplexed, Bidirectional Address/Data Bus. The addresses are present during the first portion of the bus cycle and the same pins and signal paths are used for data in the second portion of the cycle. Address/data multiplexing does not slow the access time of the DS1685 since the bus change from address to data occurs during the internal RAM access time. Addresses must be valid prior to the latter portion of ALE, at which time the DS1685/DS1687 latches the address. Valid write data must be present and held stable during the latter portion of the WR pulse. In a read cycle, the DS1685/DS1687 outputs 8 bits of data during the latter portion of the RD pulse. The read cycle is terminated and the bus returns to a high- impedance state as RD transitions high. The address/data bus also serves as a bidirectional data path for the extended RAM. 12, 16 15, 20 12 GND Ground 13 16 13 CS Chip-Select Input, Active-Low. The chip-select signal must be asserted low during a bus cycle for the RTC portion of the DS1685/DS1687 to be accessed. CS must be kept in the active state during RD and WR timing. Bus cycles that take place with ALE asserted but without asserting CS will latch addresses. However, no data transfer will occur. 14 17 14 ALE Address-Strobe Input, Active High. A pulse on the address strobe pin serves to demultiplex the bus. The falling edge of ALE causes the RTC address to be latched within the DS1685/DS1687. 15 19 15 WR Write Input, Active Low. The WR signal is an active-low signal. The WR signal defines the time period during which data is written to the addressed register. 17 21 17 RD Read Input, Active Low. RD identifies the time period when the DS1685/DS1687 drives the bus with RTC read data. The RD signal is an enable signal for the output buffers of the clock. |
Similar Part No. - DS1685Q-3 |
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Similar Description - DS1685Q-3 |
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