VULCAN Technical Manual
Detailed hardware description
© 2007 Eurotech Ltd Issue D
23
Real time clock
The RTC used on the VULCAN is the Dallas DS1302 RTC. The accuracy of the
DS1302 RTC is based on the operation of the 32.768KHz watch crystal. Its calibration
tolerance is 20ppm, which provides an accuracy of +/-1 minute per month if the
ambient temperature is +25°C. When the board is used at other temperatures, its
accuracy may be reduced, typically by -0.035ppm/
°C² ±10%. The watch crystal’s
accuracy changes by a maximum of ±3ppm in the first year, ±1ppm in the year after,
and decreases logarithmically in subsequent years. The following IXP425 GPIO pins
are used to emulate the serial I/O interface to the DS1302 RTC:
IXP425 GPIO pin
Function
GPIO 0
RTC_RST#
GPIO 1
RTC_CLK
GPIO 13
RTC_D
The DS1302 RTC also contains 31 bytes of RAM, which can be used for any data that
must be recoverable on power-up. RTC is backed by an external battery or the
onboard supercap. For details, see
, page
,
page
DS1302 RTC is also used in the tamper detect circuit. This means that if a
tamper switch is not used, a jumper is required on the J11 connector for the
RTC to operate. Without a jumper link RTC clock will stop. See
, page
.