ST20-GP6 datasheet(71/123 Pages) STMICROELECTRONICS

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ST20-GP6

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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

RTC/WDT base address + #00

Read/Write

Bit

Bit ﬁeld

Function

15:0

RTCweeks

Value of weeks counter.

Table 12.1

RTCweeks register format

RTCmilliseconds

RTC/WDT base address + #04

Read/Write

Bit

Bit ﬁeld

Function

29:0

RTCmilliseconds

Value of milliseconds counter.

Table 12.2

RTCmilliseconds register format

RTCload

RTC/WDT base address + #08

Write

Bit

Bit ﬁeld

Function

3:0

RTCload

Loads the counters with the values set in the weeks and milliseconds registers.

Write 0x0A.

Table 12.3

RTCload register format

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