st20-gp1 STMicroelectronics, st20-gp1 Datasheet - Page 63

• Manufacturer Part Number: st20-gp1
• Description: Gps Processor
• Manufacturer: STMicroelectronics

Watchdog timer
The low power alarm counter is set to operate as a watchdog timer by setting the WdEnable
register to 1. This disables entering low power mode when starting the timer. The low power alarm
is programmed and started as normal.
The WdFlag register can be read to determine if the device was reset by the notRST input or by a
watchdog time-out.
When the low power alarm counts down to the value #1, the notWdReset pin is asserted low for 1
low power clock cycle. In addition an internal reset of the ST20-GP1 is performed.
10.3 Low power configuration registers
The low power controller is allocated a 4k block of memory in the internal peripheral address
space. Information on low power mode is stored in registers as detailed in the following section.
The registers can be examined and set by the devlw (device load word) and devsw (device store
word) instructions, see Table 6.19 on page 43. Note, they can not be accessed using memory
instructions.
LPTimerLS and LPTimerMS
The LPTimerLS and LPTimerMS registers are the least significant word and most significant word
of the LPTimer register. This enables the least significant or most significant word to be written
independently without affecting the other word.
When the LPTimer register is written, the low power timer is stopped and the new value is
available to be written to the low power timer.
LPTimerStart
A write to the LPTimerStart register starts the low power timer counter. The counter is stopped
and the LPTimerStart register reset if either counter word (LPTimerLS and LPTimerMS) is
written.
Note, setting the LPTimerStart register to zero does not stop the timer.
LPTimerLS
Bit
31:0
LPTimerMS
Bit
31:0
LPTimerStart
Bit
0
Bit field
LPTimerLS
Bit field
LPTimerMS
Bit field
LPTimerStart
LPC base address + #400
LPC base address + #404
LPC base address + #408
Function
Least significant word of the low power timer.
Function
Most significant word of the low power timer.
Function
A write to this bit starts the low power timer counter.
Table 10.4 LPTimerStart register format
Table 10.3 LPTimerMS register format
Table 10.2 LPTimerLS register format
Read/Write
Read/Write
ST20-GP1
Write
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