st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 67

• Manufacturer Part Number: st20-gp6
• Description: Gps Processor
• Manufacturer: STMicroelectronics

Low power timer
The timer keeps track of real time, even when the internal clocks are stopped. The timer is a 64-bit
counter which runs off an external clock (LowPowerClockIn). This clock rate must not be more
than one eighth of the system clock rate.
Low power alarm
There is also a 40-bit low power alarm counter. A write to the LPAlarmStart register starts the low
power alarm counter and the ST20-GP6 enters low power mode. When the counter has counted
down to zero, assuming no other valid wake-up sources occur first, the ST20-GP6 exits low power
mode and the global clocks are turned back on. Whilst the clocks are turned off the LowPowerSta-
tus pin is high, otherwise it is low.
11.2 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 7.19 on page 49. 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 avail-
able 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 writ-
ten.
LPTimerLS
Bit
31:0
LPTimerMS
Bit
31:0
Bit field
LPTimerLS
Bit field
LPTimerMS
LPC base address + #400
LPC base address + #404
Function
Least significant word of the low power timer.
Function
Most significant word of the low power timer.
Table 11.2 LPTimerMS register format
Table 11.1 LPTimerLS register format
Read/Write
Read/Write
ST20-GP6
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