STV3550B STMicroelectronics, STV3550B Datasheet - Page 93

• Manufacturer Part Number: STV3550B
• Manufacturer: STMicroelectronics

Specifications of STV3550B

• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Lead Free Status / Rohs Status: Compliant

STV3550
Note:
7.3.1
7.3.2
7.4
Real time clock (RTC)
Figure 60. WDT behaviour
The counter is described as a counter that counts from zero up to the maximum allowed
number.
Clearing the counter
The watchdog counter is cleared under software control. To minimize the possibility of this
happening erroneously, there are two registers which have to be written to in order to clear
the counter. Each of these must be have the correct values (0xA and 0x5, respectively)
written to them to clear the counter.
The command registers themselves are cleared by:
●
●
●
Generation of internal watchdog reset signal
When the watchdog timer counter reaches the value of the timeout register, the internal
watchdog reset signal is asserted. This signal is also asserted asynchronously when the
external reset input to the chip is low. The internal watchdog reset signal is used to generate
a reset signal to the rest of the chip.
When the counter is reset, its timeout is reset to 2s. A clear must be performed to set a new
timeout.
The RTC provides a set of continuously running counters which can be used, with suitable
software, to provide a clock/calendar function. The counter values can be written to set the
current time/date data. The RTC is clocked by a 32.768 kHz crystal oscillator.
The RTC contains two counters:
●
●
This allows large time values to be represented with high accuracy, without the complication
of handling long (greater than 32 bit) integers in C.
Generated
Watchdog
Watchdog
Counter
notRST
Reset
Value
A successful software clear of the counter
Writing the incorrect value to either of the registers
Triggering a watchdog reset
30-bit “milliseconds” counter
16-bit “weeks” counter
Software Clears Watchdog
Software
Fails
Time
TV chassis control
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