A x e l H a r d w a r e M a n u a l
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Alarm capability
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Backup power from external battery
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±3.5ppm accuracy from -40°C to +85°C
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236 Bytes of Battery-Backed SRAM
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I²C Interface
Backup power is provided through the RTC_VBAT (J1.124)
signal. If not used, RTC_VBAT must be externally connected to
VCC.
For a detailed description of RTC characteristics, please refer
to the DS3232 datasheet.
5.9
Watchdog
An external watchdog (Maxim MAX6373) is connected to the
PORSTn signal. During normal operation, the microprocessor
should repeatedly toggle the watchdog input WDI before the
selected watchdog timeout period elapses to demonstrate that
the system is processing code properly. If the P does not
μ
provide a valid watchdog input transition before the timeout
period expires, the supervisor asserts a watchdog (WDO)
output to signal that the system is not executing the desired
instructions within the expected time frame. The watchdog
output pulse is used to reset the P. WDI is is available on
μ
AXEL connectors as WDT_WDI (J3.117).
The MAX6373 watchdog timer is pin-selectable and the timer
can be configured through the WD_SET0 (J1.67), WD_SET1
(J1.69) and WD_SET2 (J1.71) signals. As a default, the
watchdog is configured through a pull-up/pull-down resistors
network (WD_SET[2..0] = 110) that keeps the watchdog timer
inactive at startup. Startup delay ends when WDI sees its first
level transition. The default watchdog timeout period is 10 s.
The configuration can be changed by optional external circuitry
implemented on the carrier board.
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