DS1629 
 
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The real-time clock/calendar maintains a BCD count of seconds, minutes, hours, day of the week, day of 
the month,  month, and  year. It does so with an internal oscillator/ divider and a required 32.768kHz 
crystal. The end of the month date is automatically updated for months with less than 31 days, including 
compensation for leap years through the year 2100. The clock format is configurable as a 12- (power-up 
default) or 24-hour format, with an AM/PM indicator in the 12-hour mode. The RTC can be shut down 
by clearing a bit in the clock register. 
 
The crystal frequency is internally divided by a factor that the user defines. The divided output is buffered 
and can be used to clock a microcontroller. 
 
The DS1629 features an open-drain alarm output. It can be configured to activate on a thermal event, time 
event, either thermal or time, or neither thermal nor time (disabled, power-up state). The thermal alarm 
becomes  active  when  measured  temperature  is  greater  than  or  equal  to  the  value  stored  in  the  TH 
thermostat register. It will remain active until temperature is equal to or less than the value stored in TL, 
allowing for programmable hysteresis. The clock alarm will activate at the specific minute of the week 
that is programmed in the clock alarm register. The time alarm is cleared by reading from or writing to 
either the clock register or the clock alarm register. 
 
The  DS1629  configuration  register  defines  several  key  items  of  device  functionality.  It  sets  the 
conversion mode of the digital thermometer and what event, if any, will constitute an alarm condition. It 
also sets the active state of the alarm output. Finally, it enables/disables and sets the division factor for the 
oscillator output. 
 
The DS1629 also features 32 bytes of SRAM for storage of general information. This memory space has 
no bearing on thermometer or chronograph operation. Possible uses for this memory are time/temperature 
histogram storage, thermal data logging, etc. 
 
Digital data is written to/read from the DS1629 via a 2-wire interface, and all communication is MSb 
first. Individual registers are accessed by unique 8-bit command protocols. 
 
The DS1629 features a wide power supply range (2.2V d V
DD
 d 5.5V) for clock functionality, SRAM 
data retention, and 2-wire communication. EEPROM writes and temperature conversions should only be 
performed at 2.7V d V
DD
 d 5.5V for reliable results.