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BQ3285 Datasheet(PDF) 3 Page - Texas Instruments |
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BQ3285 Datasheet(HTML) 3 Page - Texas Instruments |
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3 / 22 page  DS Data strobe input When MOT = VCC, DS controls data trans- fer during a bq3285 bus cycle. During a read cycle, the bq3285 drives the bus after the rising edge on DS. During a write cycle, the falling edge on DS is used to latch write data into the chip. When MOT = VSS, the DS input is provided a signal similar to RD, MEMR, or I/OR in an Intel-based system. The falling edge on DS is used to enable the outputs during a read cycle. R/W Read/write input When MOT = VCC, the level on R/W identi- fies the direction of data transfer. A high level on R/W indicates a read bus cycle, whereas a low on this pin indicates a write bus cycle. When MOT = VSS, R/W is provided a signal similar to WR, MEMW, or I/OW in an Intel- based system. The rising edge on R/W latches data into the bq3285. CS Chip select input CS should be driven low and held stable during the data-transfer phase of a bus cy- cle accessing the bq3285. INT Interrupt request output INT is an open-drain output. INT is as- serted low when any event flag is set and the corresponding event enable bit is also set. INT becomes high-impedance whenever register C is read (see the Control/Status Registers section). SQW Square-wave output SQW may output a programmable fre- quency square-wave signal during normal (VCC valid) system operation. Any one of the 13 specific frequencies may be selected through register A. This pin is held low when the square-wave enable bit (SQWE) in register B is 0 (see the Control/Status Registers section). RCL RAM clear input A low level on the RCL pin causes the con- tents of each of the 114 storage bytes to be set to FF(hex). The contents of the clock and control registers are unaffected. This pin should be used as a user-interface input (pushbutton to ground) and not connected to the output of any active component. RCL input is only recognized when held low for at least 125ms in the presence of VCC when the oscillator is running. Using RAM clear does not affect the battery load. This pin is connected internally to a 30K Ω pull-up re- sistor. BC 3V backup cell input BC should be connected to a 3V backup cell for RTC operation and storage register non- volatility in the absence of power. When VCC slews down past VBC (3V typical), the integral control circuitry switches the power source to BC. When VCC returns above VBC, the power source is switched to VCC. Upon power-up, a voltage within the VBC range must be present on the BC pin for the oscillator to start up. RST Reset input The bq3285 is reset when RST is pulled low. When reset, INT becomes high-impedance, and the bq3285 is not accessible. Table 4 in the Control/Status Registers section lists the register bits that are cleared by a reset. Reset may be disabled by connecting RST to VCC. This allows the control bits to re- tain their states through power- down/power-up cycles. X1–X2 Crystal inputs The X1–X2 inputs are provided for an ex- ternal 32.768Khz quartz crystal, Daiwa DT-26 or equivalent, with 6pF load capaci- tance. A trimming capacitor may be neces- sary for extremely precise time-base gen- eration. In the absence of a crystal, an oscillated output of 32.768kHz can be fed into the X1 input. 3 Jan. 1999 E bq3285 |
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