NXP Semiconductors MC9S08PA4, Reference Manual

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• Provides robust check that program flow is faster than expected
• Early refresh attempts trigger a reset.
• Optional timeout interrupt to allow post-processing diagnostics
• Interrupt request to CPU with interrupt vector for an interrupt service routine
(ISR)
• Forced reset occurs 128 bus clocks after the interrupt vector fetch.
• Configuration bits are write-once-after-reset to ensure watchdog configuration cannot
be mistakenly altered.
• Robust write sequence for unlocking write-once configuration bits
• Unlock sequence of writing 0xC520 and then 0xD928 within 16 bus clocks for
allowing updates to write-once configuration bits
• Software must make updates within 128 bus clocks after unlocking and before
WDOG closing unlock window.
17.1.2 Block diagram
The following figure provides a block diagram of the WDOG module.
MUX
MUX
MUX
32K CLK
EXT CLK
UPDATE
EN
CLK PRES WIN INT
1K CLK
BUS CLK
256
16-bit Window Register
0xD928
0xC520 Control Status
128 Bus Cycle
Disable Protect
Bit Write Control
Protect
Window
Reset
Counter
Overflow
Counter
Write Control
0xA602
0xB480
16-bit Timeout Value Register
Refresh Sequence
Compare Logic
16-bit Counter Register
Compare Logic
Control
Logic
128 Bus CPU Reset
IRQ Interrupt
Clock Delay
Backup Reset
Figure 17-1. WDOG block diagram
Introduction
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
336 NXP Semiconductors