System Configuration and Protection
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
6-21
Figure 6-8. PIT Block Diagram
The timeout period is calculated as:
Solving this equation using a 4-MHz external clock and a pre-divider of 256 gives:
This gives a range from 64 microseconds, with a PITC of 0x0000, to 4.19 seconds, with a PITC of 0xFFFF.
When a 20-MHz crystal is used with a pre-divider of 256, the range is between 12.8 microseconds to 0.84
seconds.
6.1.10
Software Watchdog Timer (SWT)
The software watchdog timer (SWT) prevents system lockout in case the software becomes trapped in
loops with no controlled exit. The SWT is enabled after system reset to cause a system reset if it times out.
The SWT requires a special service sequence to be executed on a periodic basis. If this periodic servicing
action does not occur, the SWT times out and issues a reset or a non-maskable interrupt (NMI), depending
on the value of the SWRI bit in the SYPCR register.
The SWT can be disabled by clearing the SWE bit in the SYPCR. Once the SYPCR is written by software,
the state of the SWE bit cannot be changed.
The SWT service sequence consists of the following two steps:
1. Write 0x556C to the software service register (SWSR)
2. Write 0xAA39 to the SWSR
The service sequence clears the watchdog timer and the timing process begins again. If any value other
than 0x556C or 0xAA39 is written to the SWSR, the entire sequence must start over.
Clock
16-bit
PITC
PITRTCLK
PS (PISCR)
PIE (PISCR)
PIT
PTE
Disable
Clock
Modulus
Counter
Interrupt
PITF (PISCR)
(PISCR)
(PISCR)
PIT
PERIOD
PITC
1
+
F
PITRTCLK
-----------------------------------
PITC
1
+
ExternalClock
4 or 256
-----------------------------------------
〈
〉
-----------------------------------------------
=
=
PIT
PERIOD
PITC
1
+
15625
------------------------
=
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...