Intermec 074787-001 User Manual
Chapter 2 — Theory of Operation
PB42 Portable Receipt Printer Service Manual
31
Printhead Power Switch Control Logic
Watchdog Timer
The PowerPC microprocessor has a watchdog timer function. The
watchdog timer automatically resets the processor after a pre-determined
time period if a specific set of instructions are not executed. In case there is
a software lock-up condition caused by some unforeseen event (such as
ESD) this function should be enabled.
watchdog timer automatically resets the processor after a pre-determined
time period if a specific set of instructions are not executed. In case there is
a software lock-up condition caused by some unforeseen event (such as
ESD) this function should be enabled.
Section 10.7 of the MPC885 Reference Manual describes the watchdog
timer in detail.
timer in detail.
To configure the watchdog timer set SYPCR[SWF, SWE, SWRI, SWP] to
1111. The timer period is determined by the 16 bit field, SYPCR[SWTC]
and is calculated by the following formula:
1111. The timer period is determined by the 16 bit field, SYPCR[SWTC]
and is calculated by the following formula:
SYPCR[SWTC] = clock frequency
*
timeout period / 2048
The maximum timeout period with a 66MHz clock is 2.034 seconds.
Once enabled, the software must issue the following instructions, in the
given order, within the timeout period:
given order, within the timeout period:
1
Write 0x556C to the software service register. (SWSR)
2
Write 0xAA39 to the SWSR.
Although the writes must occur in the correct order before a timeout
occurs, any number of instructions may be executed between the writes.
This allows interrupts and exceptions to occur between the two writes when
necessary.
occurs, any number of instructions may be executed between the writes.
This allows interrupts and exceptions to occur between the two writes when
necessary.