DS1284 watchdog timekeeper chip DS1284 022798 1/3 features ? keeps track of hundredths of seconds, seconds, min- utes, hours, days, date of the month, months, and years; valid leap year compensation up to 2100 ? watchdog timer restarts an outofcontrol processor ? alarm function schedules real-time related activities ? programmable interrupts and square wave outputs maintain 28pin jedec footprint ? all registers are individually addressable via the ad- dress and data bus ? accuracy is better than 2 minute/month at 25 c ? 50 bytes of user nv ram ? optional 28pin plcc surface mount package ? lowpower cmos circuitry is maintained on less than 0.5 m a when power is supplied from battery input ? optional industrial temperature range available on 28pin plcc (40 c to +85 c) pin assignment 1 2 3 4 5 6 7 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 8 25 26 27 28 nc gnd v cc sqw v bat x1 x2 43 2 282726 25 24 23 22 21 20 19 5 6 7 8 9 10 11 12 13 14 15 16 17 18 a5 a4 a3 a2 a1 a0 dq0 dq7 gnd sqw vbat 1 gnd inta we intb (intb) oe ce rclr rclr oe ce nc x2 x1 inta vcc we intb(intb) dq1 dq2 gnd dq3 dq4 dq5 dq6 DS1284 28pin dip (600 mil) DS1284q 28pin plcc dq7 dq6 dq5 dq4 dq3 dq2 dq1 a5 a4 a3 a2 a1 a0 dq0 pin description inta interrupt output a (open drain) intb (intb) interrupt output b (open drain) a0a5 address inputs dq0dq7 data input/output ce chip enable oe output enable we write enable v cc +5 volts gnd ground nc no connection sqw square wave output x1,x2 32.768 khz crystal connections v bat +3 volt battery input rclr ram clear description the DS1284 watchdog timekeeper chip is a selfcon- tained realtime clock, alarm, watchdog timer, and inter- val timer in a 28pin jedec dip package or a 28pin plcc surface mount package. an external crystal and battery are the only components required to maintain timeofday and memory status in the absence of power. for a complete description of operating condi- tions, electrical characteristics, bus timing, and pin de- scriptions other than x1, x2, v bat , and rclr , see the ds1286 watchdog timekeeper data sheet.
DS1284 022798 2/3 pin description x1, x2 connections for a standard 32.768 khz quartz crystal. the internal oscillator circuitry is designed for operation with a crystal having a specified load capaci- tance (c l ) of 6 pf. the crystal is connected directly to the x1 and x2 pins. there is no need for external capac- itors or resistors. for more information on crystal selec- tion and crystal layout considerations, please consult application note 58, acrystal considerations with dal- las real time clockso. v bat battery input for any standard 3-volt lithium cell or other energy source. battery voltage must be held be- tween 2.4 and 3.7 volts for proper operation. the nomi- nal write protect trip point voltage at which access to registers containing time, watchdog, alarm, and ram information is denied is set by internal circuitry as 1.26 x v bat . a maximum load of 0.5 m a at 25 c in the absence of power should be used to size the external energy source. the battery should be connected directly to the v bat pin. a diode must not be placed in series with the battery to the v bat pin. furthermore, a diode is not nec- essary because reverse charging current protection cir- cuitry is provided internal to the device and has passed the requirements of underwriters laboratories for ul listing. an optional ground pin is provided for connec- tion to battery negative. this pin should be grounded but can be left floating. rclr the rclr pin is used to clear (set to logic 1) all 50 bytes of user nv ram but does not affect the regis- ters involved with time, alarm, and watchdog functions. in order to clear the ram, rclr must be forced to an input logic zero (0. 3 to +0.8 volts) during battery back- up mode when v cc is not applied. the rclr function is designed to be used via human interface (shorting to ground or by switch) and not be driven with external buff- ers. this pin is internally pulled up and should be left floating when not in use. DS1284q 28pin plcc watchdog timekeeper d 45deg. cl d e f h a b b1 d2 dim min max 28pin pkg a in. mm b in. mm d in. mm d2 in. mm e in. mm e2 in. mm f in. mm h in. mm 7.62 0.442 17.68 0.462 11.73 0.480 12.2 0.500 12.7 0.390 9.91 0.430 10.92 0.090 2.29 0.120 3.05 0.390 9.91 0.430 10.92 0.015 0.38 0.020 0.518 0.100 2.54 0.020 0.518 0.300 bsc e2 a3
DS1284 022798 3/3 DS1284 28pin dip watchdog timekeeper 1 c a b h j k g e f dim min max 28pin pkg a in. mm b in. mm c in. mm d in. mm e in. mm f in. mm g in. mm h in. mm j in. mm k in. mm 1.445 1.470 0.530 0.550 0.140 0.160 0.600 0.625 0.015 0.040 0.120 0.145 0.090 0.110 0.625 0.675 0.008 0.012 0.015 0.022 d
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