Backup Watchdog Timer (BWT) Module
MCF52110 ColdFire® Integrated Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
7-5
Preliminary
7.2.2.4
Backup Watchdog Timer Service Register (WSR)
, and is used to instruct the BWT to reset its internal counter to the value
in WMR[WM]. This is known as servicing the BWT. To do so, the software must write the two values
0x5555 and 0xAAAA, in that order, to WSR. These two write operations must be completed before the
BWT timeout period is reached (i.e., WCNTR[WC] reaches zero). If these operations are not completed
before the end of the timeout period, the BWT asserts a system reset.
The software can execute other instructions between the two write instructions required to service the
BWT (0x5555 and 0xAAAA). All instructions, however, must be completed before the timeout period is
reached to prevent a reset.
Writing any values other than 0x5555 or 0xAAAA to the WSR resets the servicing sequence. The software
must then begin the sequence again (writing 0x5555 and 0xAAAA to WSR) to service the BWT.
This register must be written as a whole.
IPSBAR
Offset: 0x14_0004 (WCNTR)
Access: Supervisor read/write
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
WC
W
Reset
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Figure 7-4. Backup Watchdog Timer Count Register (WCNTR)
Table 7-4. WCNTR Field Descriptions
Field
Description
15–0
WC
BWT counter. This field reflects the current value in the BWT counter.
IPSBAR
Offset: 0x14_0006 (WSR)
Access: Supervisor read/write
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
WS
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 7-5. Backup Watchdog Timer Service Register (WSR)
Table 7-5. WSR Field Descriptions
Field
Description
15–0
WS
BWT service field. To service the BWT, the software must write the values 0x5555 and 0xAAAA, in that order, to this
field before the BWT timeout period is reached.
