Datasheet

NMIFLG[NMINT]
1
0
Generate
Interrupt
Pulse
When
Input=1
NMINT
Latch
Clear
Set
Clear
NMIFLGCLR[NMINT]
XRS
0
NMICFG[CLOCKFAIL]
Latch
Clear
Set
Clear
XRS
NMIFLG[CLOCKFAIL]
NMIWatchdog
SYSCLKOUT
SYSRS
NMIRS
NMIWDPRD[15:0]
NMIWDCNT[15:0]
NMIFLGCLR[CLOCKFAIL]
SYNC?
NMIFLGFRC[CLOCKFAIL]
SYSCLKOUT
SeeSystem
ControlSection
CLOCKFAIL
TMS320F28030, TMS320F28031, TMS320F28032
TMS320F28033, TMS320F28034, TMS320F28035
www.ti.com SPRS584J –APRIL 2009–REVISED OCTOBER 2013
Figure 3-12. NMI-watchdog
3.7.5 CPU-Watchdog Module
The CPU-watchdog module on the 2803x 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 3-13 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 (that is, 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.
Copyright © 2009–2013, Texas Instruments Incorporated Functional Overview 53
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