ata6616 ATMEL Corporation, ata6616 Datasheet - Page 60

• Manufacturer Part Number: ata6616
• Description: Microcontroller With Lin Transceiver, 5v Regulator And Watchdog
• Manufacturer: ATMEL Corporation

4.5.3.8
60
ATA6616/ATA6617 [Preliminary]
Clock Monitoring
A safe system needs to monitor its clock sources. Two domains need to be monitored:
In the first domain, the user (code) can easily check the validity of the clock(s)
Command” on page
In the second domain, the lack of a clock results in the code not running. Thus, the presence of
the system clock needs to be monitored by hardware.
Using the on-chip watchdog allows this monitoring. Normally, the watchdog reloading is per-
formed only if the code reaches some specific software labels, reaching these labels proves that
the system clock is running. Otherwise the watchdog reset is enabled. This behavior can be con-
sidered as a clock monitoring.
If the standard watchdog functionality is not desired, the ATtiny167 watchdog permits the sys-
tem clock to be monitored without having to resort to the complexity of a full software watchdog
handler. The solution proposed in the ATtiny167 is to automate the watchdog reloading with only
one command, at the beginning of the session.
So, to monitor the system clock, the user will have two options:
The two options are exclusive.
Warning:
These two options make sense ONLY if the clock source at RESET is an INTERNAL SOURCE.
The fuse settings determine this operation.
Figure 4-15. Watchdog Timer with Automatic Reloading
The ‘Enable Watchdog in Automatic Reload Mode’ command has priority over the standard
watchdog enabling. In this mode, only the reset function of the watchdog is enabled (no more
watchdog interrupt). The WDP3..0 bits of the WDTCSR register always determine the watchdog
timer prescaling.
As the watchdog will not be active before executing the ‘Enable Watchdog in Automatic Reload
Mode’ command, it is recommended to activate this command before switching to an external
clock source (See following notes).
• Clock sources for peripherals,
• Clocks sources for system clock generation.
1. Using the standard watchdog features (software reload),
2. Or using the automatic reloading (hardware reload).
WDTCSR
Interrupt
Register:
Reset
WD
WD
58.).
Internal Bus
WatchDog
Reload
0
DRAFT
1
Checker
WatchDog Clock
Enable
Automatic
Reloading
Mode
System CLK
9132A–AUTO–10/08
(See “COUT