TMP320C2811PBKA datasheet(48/147 Pages) TI

48 / 147 page

Functional Overview

June 2004

SPRS257

3.7.5

Watchdog Block

The watchdog block on R281x is identical to the one used on the 240x 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. Figure 3−10 shows the various functional blocks within the watchdog module.

/512

OSCCLK

WDCR (WDPS(2:0))

WDCLK

WDCNTR(7:0)

WDKEY(7:0)

Bad Key

Good Key

WDCR (WDCHK(2:0))

Bad

WDCHK

Key

WDCR (WDDIS)

Clear Counter

SCSR (WDENINT)

Watchdog

Prescaler

Generate

Output Pulse

(512 OSCCLKs)

8-Bit

Watchdog

Counter

CLR

WDRST

WDINT

Watchdog

55 + AA

Key Detector

XRS

Core-reset

NOTE A: The WDRST signal is driven low for 512 OSCCLK cycles.

WDRST

(See Note A)

Internal

Pullup

Figure 3−10. Watchdog Module

The WDINT signal enables the watchdog to be used as a wakeup from IDLE/STANDBY mode timer.

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 the PLL clock or the oscillator clock. The WDINT signal

is fed to the LPM block so that it can wake the device from STANDBY (if enabled). See Section 3.7.6,

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.

3.7.6

Low-Power Modes Block

The low-power modes on R281x are similar to the 240x devices. Table 3−14 summarizes the various modes.

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