st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 71

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

The watchdog timer function is enabled by an external pin (WdEnable). If this pin is held low, then
a watchdog reset will not occur.
12.4 RTC/WDT configuration registers
The RTC/WDT has a number of registers which can be accessed by the CPU. The function of
these registers is described below.
RTCweeks register
The RTCweeks register contains the value of the weeks counter.
RTCmilliseconds register
The RTCmilliseconds register contains the value of the milliseconds counter.
RTCload register
A write to the RTCload register loads the weeks and milliseconds counters with the values cur-
rently set in the RTCweeks and RTCmilliseconds registers.
To minimize the possibility of the counters being erroneously updated by rogue software, the
counters are only loaded if the correct value (0xA) is written to the RTCload register. This register
is cleared when the load takes place. It is also cleared when the system is reset.
In addition, the load operation is only enabled if both the milliseconds and weeks registers have
had values written to them since the last load of the counters (or since the system was reset).
RTCstatus register
The RTCstatus register contains RTC status information.
To avoid the milliseconds and weeks counters being loaded with inconsistent values, the millisec-
onds and weeks registers must not be modified until the update of the counters has completed. To
enable software to detect this situation a status bit is provided in the RTCstatus register to indicate
RTCweeks
Bit
RTCmilliseconds
Bit
RTCload
Bit
15:0
29:0
3:0
Bit field
Bit field
Bit field
RTCweeks
RTCmilliseconds
RTCload
Table 12.2 RTCmilliseconds register format
Function
Value of weeks counter.
Function
Value of milliseconds counter.
Function
Loads the counters with the values set in the weeks and milliseconds registers.
Write 0x0A.
Table 12.1 RTCweeks register format
Table 12.3 RTCload register format
RTC/WDT base address + #00
RTC/WDT base address + #04
RTC/WDT base address + #08
Read/Write
Read/Write
ST20-GP6
Write
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