Real-Time Clocks

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9

Pin Description (continued)

PIN

24

28

NAME

FUNCTION

21

3

RCLR

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

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.

22

4

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

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

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

23

5

SQW

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

24

6, 7

are inhibited.

2, 3, 16,

20

(DS17x87

only)

11, 18

N.C.

No Connection