19.4.9 WDT Postscalers

The WDT has a 5-bit postscaler to create a wide variety of time-out periods. This postscaler provides 1:1 through 1:1048576 divider ratios (see the following table). Time-out periods that range between 1 ms and 1048.576 seconds (nominal) can be achieved using the postscaler.

Table 19-1. WDT Time-out Period versus Postscaler Settings^(1),(2)
WDTPSR[4:0]/WDTPSS[4:0]	Postscaler Ratio	Time-out Period (Non-windowed Mode)	Time-out Period (Programmable Windowed Mode)⁽³⁾
`00000`	1:1	1 ms	0.75 ms
`00001`	1:2	2 ms	1.5 ms
`00010`	1:4	4 ms	3 ms
`00011`	1:8	8 ms	6 ms
`00100`	1:16	16 ms	12 ms
`00101`	1:32	32 ms	24 ms
`00110`	1:64	64 ms	48 ms
`00111`	1:128	128 ms	96 ms
`01000`	1:256	256 ms	192 ms
`01001`	1:512	512 ms	384 ms
`01010`	1:1024	1.024s	0.768s
`01011`	1:2048	2.048s	1.536s
`01100`	1:4096	4.096s	3.072s
`01101`	1:8192	8.192s	6.144s
`01110`	1:16384	16.384s	12.228s
`01111`	1:32768	32.768s	24.576s
`10000`	1:65536	65.536s	49.152s
`10001`	1:131072	131.072s	98.304s
`10010`	1:262144	262.144s	196.608s
`10011`	1:524288	524.288s	393.216s
`10100`	1:1045876	1048.576s	786.432s
Note: All other combinations result in operation as if the postscaler was set to ‘`10100`’. The periods listed are based on a 32 kHz (nominal) input clock. In this case, DEVCFG2.WINSZ = `00`. The WDT window is 75% of the selected WDT period.

The settings are chosen using the DEVCFG2.WDTPSR[4:0] inputs for the Run mode counter and the DEVCFG1.WDTPSS[4:0] inputs for the Standby Sleep mode counter. The time-out period of the WDT is calculated as shown in the following equation:

WDTPeriod = 1 ms• 2 ^Postscaler