DS17485-5 查看數據表（PDF） - Maxim Integrated

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产品描述 (功能)

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DS17485-5

Real-Time Clocks

Maxim Integrated 

DS17285/DS17287/

DS17485/DS17487/

DS17885/DS17887

Real-Time Clocks

Pin Description (continued)

PIN

24

28

NAME

FUNCTION

Active-Low RAM Clear Input. This pin is used to clear (set to logic 1) all the 114 bytes of

general-purpose RAM but does not affect the RAM associated with the real time clock or

21

3

RCLR

extended RAM. RCLR may be invoked while the part is powered from any supply. The RCLR

function is designed to be used via a human interface (shorting to ground manually or by a

switch) and not to be driven with external buffers. This pin is internally pulled up. Do not use an

external pullup resistor on this pin.

Auxiliary Battery Input. Required for kickstart and wake-up functions. This input also supports

clock/calendar and user RAM if VBAT is at lower voltage or is not used. A standard +3V lithium

cell or other energy source can be used. Diodes placed in series between VBAUX and the

22

4

VBAUX

battery may prevent proper operation. UL recognized to ensure against reverse charging

current when used with a lithium battery (www.maximintegrated.com/qa/info/ul/). For 3V

VCC operation, VBAUX must be held between +2.5V and +3.7V. For 5V VCC operation, VBAUX

must be held between +2.5V and +5.2V. If VBAUX is not used it should be grounded and the

auxiliary-battery-enable bit bank 1, register 4BH, should = 0.

23

5

24

6, 7

2, 3,

16, 20

(DS17x87

only)

11, 18

SQW

VCC

Square-Wave Output. When VCC rises above VPF, bits DV1 and E32k are set to 1. This

condition enables a 32kHz square-wave output. A square wave is output if either SQWE = 1

or E32k = 1. If E32k = 1, then 32kHz is output regardless of the other control bits. If E32k =

0, then the output frequency is dependent on the control bits in Register A. The SQW pin can

output a signal from one of 13 taps provided by the 15 internal divider stages of the RTC. The

frequency of the SQW pin can be changed by programming Register A, as shown in Table 3.

The SQW signal can be turned on and off using the SQWE bit in Register B or the E32k bit

in extended register 4Bh. A 32kHz square wave is also available when VCC is less than VPF

if E32k = 1, ABE = 1, and voltage is applied to the VBAUX pin. When disabled, SQW is high

impedance when VCC is below VPF.

DC Power Pin for Primary Power Supply. When VCC is applied within normal limits, the device

is fully accessible and data can be written and read. When VCC is below VPF reads and writes

are inhibited.

N.C. No Connection

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