System Configuration and Protection
MPC561/MPC563 Reference Manual, Rev. 1.2
6-22
Freescale Semiconductor
Although the writes must occur in the correct order prior to time-out, any number of instructions may be
executed between the writes. This allows interrupts and exceptions to occur, if necessary, between the two
writes.
Figure 6-9. SWT State Diagram
Although most software disciplines support the watchdog concept, different systems require different
time-out periods. For this reason, the software watchdog provides a selectable range for the time-out
period.
, the range is determined by the value in the SWTC field. The value held in the SWTC field
is then loaded into a 16-bit decrementer clocked by the system clock. An additional divide by 2048
prescaler is used if necessary. The decrementer begins counting when loaded with a value from the
software watchdog timing count field (SWTC). After the timer reaches 0x0, a software watchdog
expiration request is issued to the reset or NMI control logic.
Upon reset, the value in the SWTC is set to the maximum value and is again loaded into the software
watchdog register (SWR), starting the process over. When a new value is loaded into the SWTC, the
software watchdog timer is not updated until the servicing sequence is written to the SWSR. If the SWE
is loaded with the value zero, the modulus counter does not count (i.e. SWTC is disabled).
0x556C/Don’t Reload
Reset
0xAA39/Reload
State 0
Waiting for 0x556C
State 1
Waiting for 0xAA39
Not 0xAA39/Don’t Reload
Not 0x556C/Don’t Reload
Not 0x556C/Don’t Reload
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...