Atmel XMEGA B, User Manual, Page: 115 / 415

115 XMEGA B [DATASHEET]
8291B–AVR–01/2013
10.7 Registers Description
10.7.1 CTRL – Control register
 Bits 7:6 – Reserved
These bits are unused and reserved for future use. For compatibility with future devices, always write these bits to zero
when this register is written.

Bits 5:2 – PER[3:0]: Timeout Period
These bits determine the watchdog timeout period as a number of 1kHz ULP oscillator cycles. In window mode
operation, these bits define the open window period. The different typical timeout periods are found in
Table 10-1 . The
initial values of these bits are set by the watchdog timeout period (WDP) fuses, which are loaded at power-on.
In order to change these bits, the CEN bit must be written to 1 at the same time. These bits are protected by the
configuration change protection mechanism. For a detailed description, refer to
“Configuration Change Protection” on
page 13 .
Table 10-1. Watchdog timeout periods
Bit 7 6 5 4 3 2 1 0
+0x00
– – PER[3:0] ENABLE CEN
Read/Write (unlocked) R R R/W R/W R/W R/W R/W R/W
Read/Write (locked) R R R R R R R R
Initial Value (x = fuse) 0 0 X X X X X 0
PER[3:0] Group Configuration Typical Timeout Periods
0000 8CLK 8ms
0001 16CLK 16ms
0010 32CLK 32ms
0011 64CLK 64ms
0100 128CLK 0.128s
0101 256CLK 0.256s
0110 512CLK 0.512s
0111 1KCLK 1.0s
1000 2KCLK 2.0s
1001 4KCLK 4.0s
1010 8KCLK 8.0s
1011 – Reserved
1100 – Reserved
1101 – Reserved
1110 – Reserved
1111 – Reserved