TMS320F28027 Datasheet, PDF (44/130 Pages) Texas Instruments – Piccolo Microcontrollers

TMS320F28027, TMS320F28026, TMS320F28023, TMS320F28022
TMS320F28021, TMS320F28020, TMS320F280200
SPRS523F – NOVEMBER 2008 – REVISED DECEMBER 2010
NMIFLGCLR[NMINT]
NMIFLG[NMINT]
Clear
Latch
Set _Clear
XRS
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NMINT
Generate
Interrupt
Pulse
When
Input = 1
1
0 ^{NMIFLG[CLOCKFAIL]}
Clear
NMIFLGCLR[CLOCKFAIL]
0
Latch
SYNC? ^CLOCKFAIL
Clear ^Set
SYSCLKOUT
NMICFG[CLOCKFAIL]
XRS
NMIFLGFRC[CLOCKFAIL]
NMIWDPRD[15:0]
NMIWDCNT[15:0]
SYSCLKOUT
SYSRS
NMI Watchdog
NMIRS
Figure 3-14. NMI-watchdog
See System
Control Section
3.8.5 CPU-Watchdog Module
The CPU-watchdog module on the 2802x device is similar to the one used on the 281x/280x/283xx
devices. This module generates an output pulse, 512 oscillator clocks wide (OSCCLK), whenever the 8-bit
watchdog up counter has reached its maximum value. To prevent this, the user must disable the counter
or the software must periodically write a 0x55 + 0xAA sequence into the watchdog key register that resets
the watchdog counter. Figure 3-15 shows the various functional blocks within the watchdog module.
Normally, when the input clocks are present, the CPU-watchdog counter decrements to initiate a
CPU-watchdog reset or WDINT interrupt. However, when the external input clock fails, the CPU-watchdog
counter stops decrementing (i.e., the watchdog counter does not change with the limp-mode clock).
NOTE
The CPU-watchdog is different from the NMI watchdog. It is the legacy watchdog that is
present in all 28x devices.
NOTE
Applications in which the correct CPU operating frequency is absolutely critical should
implement a mechanism by which the MCU will be held in reset, should the input clocks ever
fail. For example, an R-C circuit may be used to trigger the XRS pin of the MCU, should the
capacitor ever get fully charged. An I/O pin may be used to discharge the capacitor on a
periodic basis to prevent it from getting fully charged. Such a circuit would also help in
detecting failure of the flash memory.
44
Functional Overview
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