mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 296

• Manufacturer Part Number: mpc823rg
• Description: Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
• Manufacturer: Freescale Semiconductor, Inc

The decrementer begins counting when it is loaded with a value from the SWTC field. After
the timer reaches 0x0, a software watchdog expiration request is issued to the reset or NMI
control logic. At reset, the value in the SWTC register is set to the maximum value and is
loaded into the software watchdog register (SWR) again, thus starting the process over.
When a new value is loaded into the SWTC register, the software watchdog timer will not be
updated until the servicing sequence is written to the SWSR register. If the SWE bit is loaded
with the value 0, the modulus counter will not count.
12.9.1 Software Service Register
The software service register (SWSR) is the location that the software watchdog timer
servicing sequence writes to. To prevent a SWT timeout, a write of 0x556C followed by
0xAA39 must be written to this register. The SWSR can be written at any time, but returns
all zeros when read.
SEQ—Sequence
This field is the pattern that is used to control the state of the software watchdog timer.
SWSR
RESET
FIELD
ADDR
R/W
BIT
CLOCK
CORE
0
1
Figure 12-7. Software Watchdog Timer Block Diagram
DISABLE
CLOCK
2
SWE
FRZ
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5
SERVICE
SWSR
LOGIC
(IMMR & 0xFFFF0000) + 0x00E
6
MUX
SWP
7
SEQ
W
0
8
SWR / DECREMENTER
RELOAD
9
ROLLOVER = 0
16-BIT
10
SWTC
11
System Interface Unit
TIMEOUT
12
RESET
OR NMI
13
14
12-27
15