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SPRS230M – OCTOBER 2003 – REVISED MARCH 2011
3.6.2
Watchdog Block
The watchdog block on the 280x is similar to the one used on the 240x and 281x devices. The watchdog
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 disables the counter or the software
must periodically write a 0x55 + 0xAA sequence into the watchdog key register which will reset the
watchdog counter.
shows the various functional blocks within the watchdog module.
WDCR (WDPS[2:0])
WDCR (WDDIS)
WDCNTR[7:0]
OSCCLK
/512
Watchdog
Prescaler
WDCLK
8-Bit
Watchdog
Counter
CLR
Clear Counter
Internal
Pullup
WDKEY[7:0]
Watchdog
55 + AA
Key Detector
XRS
Core-reset
WDCR (WDCHK[2:0])
Bad
WDCHK
Key
SCSR (WDENINT)
Generate
Output Pulse
(512 OSCCLKs)
WDRST
WDINT
Good Key
WDRST
(A)
1
0
1
A.
The WDRST signal is driven low for 512 OSCCLK cycles.
Figure 3-14. Watchdog Module
The WDINT signal enables the watchdog to be used as a wakeup from IDLE/STANDBY mode.
In STANDBY mode, all peripherals are turned off on the device. The only peripheral that remains
functional is the watchdog. The WATCHDOG module will run off OSCCLK. The WDINT signal is fed to the
LPM block so that it can wake the device from STANDBY (if enabled). See
Low-Power
Modes Block, for more details.
In IDLE mode, the WDINT signal can generate an interrupt to the CPU, via the PIE, to take the CPU out of
IDLE mode.
In HALT mode, this feature cannot be used because the oscillator (and PLL) are turned off and hence so
is the WATCHDOG.
Copyright © 2003–2011, Texas Instruments Incorporated
Functional Overview
51
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