Datasheet

20.6.7 Synchronization
Due to asynchronicity between the main clock domain and the peripheral clock domains, some registers
need to be synchronized when written or read.
The following registers are synchronized when written:
• Enable bit in Control A register (CTRLA.ENABLE)
• Window Enable bit in Control A register (CTRLA.WEN)
• Always-On bit in control Control A (CTRLA.ALWAYSON)
• Watchdog Clear register (CLEAR)
Required write synchronization is denoted by the "Write-Synchronized" property in the register
description.
Required read synchronization is denoted by the "Read-Synchronized" property in the register
description.
20.6.8 Additional Features
20.6.8.1 Always-On Mode
The Always-On mode is enabled by setting the Always-On bit in the Control A register
(CTRLA.ALWAYSON=1). When the Always-On mode is enabled, the WDT runs continuously, regardless
of the state of CTRLA.ENABLE. Once written, the Always-On bit can only be cleared by a power-on
reset. The Configuration (CONFIG) and Early Warning Control (EWCTRL) registers are read-only
registers while the CTRLA.ALWAYSON bit is set. Thus, the time period configuration bits (CONFIG.PER,
CONFIG.WINDOW, EWCTRL.EWOFFSET) of the WDT cannot be changed.
Enabling or disabling Window mode operation by writing the Window Enable bit (CTRLA.WEN) is allowed
while in Always-On mode, but note that CONFIG.PER cannot be changed.
The Interrupt Clear and Interrupt Set registers are accessible in the Always-On mode. The Early Warning
interrupt can still be enabled or disabled while in the Always-On mode, but note that
EWCTRL.EWOFFSET cannot be changed.
Table WDT Operating Modes With Always-On shows the operation of the WDT for
CTRLA.ALWAYSON=1.
Table 20-2. WDT Operating Modes With Always-On
WEN Interrupt Enable Mode
0 0 Always-on and normal mode
0 1 Always-on and normal mode with Early Warning interrupt
1 0 Always-on and window mode
1 1 Always-on and window mode with Early Warning interrupt
20.6.8.2 Early Warning
The Early Warning interrupt notifies that the WDT is approaching its time-out condition. The Early
Warning interrupt behaves differently in Normal mode and in Window mode.
In Normal mode, the Early Warning interrupt generation is defined by the Early Warning Offset in the
Early Warning Control register (EWCTRL.EWOFFSET). The Early Warning Offset bits define the number
of CLK_WDT_OSC clocks before the interrupt is generated, relative to the start of the watchdog time-out
period.
SAM D5x/E5x Family Data Sheet
WDT – Watchdog Timer
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 271