VULCAN Technical Manual
Detailed hardware description
© 2007 Eurotech Ltd Issue D
24
Tamper detect circuit
When the VULCAN is fitted in the ICE enclosure, the tamper detect switch is mounted
onto the side of the enclosure in such a position that it is activated when the lid is
opened. The switch is connected to the tamper connector J11. Once the tamper detect
software has been invoked, any attempt to remove this assembly activates the tamper
detect system. The VULCAN tamper detect circuit is implemented using the DS1302
RTC incorporating a 31 byte battery-backed non-volatile RAM. The RTC is backed up
by a super capacitor giving maximum memory retention of 5 days.
The tamper detect software stores a unique pattern in the RTC RAM, which is cleared
when the tamper detect system is activated. Any tamper detect activity (in either a
powered or non-powered situation) cuts the power supply to the RTC and clears the
contents of the DS1302 RAM and a CLOCK HALT bit within the device. This single bit
is not battery-backed and is guaranteed to activate once the RTC power supply voltage
drops below 2.0V. A concatenation of the CLOCK HALT bit and the contents of the
RAM fully ensure tamper activity detection.
If the tamper detect circuit is not used, pins 1 and 2 of connector J11 must be
connected together using a jumper, to provide a power supply to DS1302 RTC. For
more information, see
, page
Diagram of tamper switch and J11 connections is shown below.
RTC_PWR
3V3
GND
J11
1
2
3
TAMPER SWITCH
2
1
3