11-22
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part III. Configuration
the value in SWTC is set to the maximum value and is loaded into the software watchdog
down-counter, starting the process.
Although most software disciplines permit or encourage the watchdog concept, some
systems require a selection of timeout periods. For this reason, the software watchdog timer
provides a selectable range for the timeout period. Figure 11-16 shows the method for
handling this need. When a new value is loaded into SWTC, the software watchdog timer
is not updated until the servicing sequence is written to SWSR. If the SWE bit is loaded
with a zero, the modulus counter will not count.
Figure 11-16. Software Watchdog Timer Block Diagram
11.7.1 Software Service Register (SWSR)
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 should be written to this register. The SWSR can be written at any time, but returns
all zeros when read.
Bit
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Field
SEQ
Reset
0000_0000_0000_0000
R/W
W
Addr
(IMMR & 0xFFFF0000) + 0x00E
Figure 11-17. Software Service Register (SWSR)
Clock
Disable
Timeout
Core
Clock
Reload
16-Bit
MUX
SWP
SWE
SWSR
Divide
by 2,048
Service
Logic
FRZ
Down-counter
Rollover = 0
SWTC
HRESET
or NMI
Содержание MPC860 PowerQUICC
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