TNETV2840ENGGU datasheet(49/91 Pages) TI1

49 / 91 page

Functional Overview

December 1999 − Revised October 2008

SPRS122F

The registers WDTIM, WDPRD, WDTCR, and the PREMD bit in WDTSCR must be configured before the

watchdog enters the active state. By default, WDTIM =FFFFh, WDPRD = FFFFh, PREMD = 1, TDDR = 1111b.

Writing a ‘1’ to WDEN and configuring the PREMD bit must be done at the same time that A7Eh is written to

WDKEY in watchdog pre-active state.

3.2.5.6

Watchdog State Diagram

Figure 3−25 shows the watchdog operation state diagram.

Initial State

(Watchdog

Disabled)

(WDTIM=FFFFh)

(WDPRD=FFFFh)

(TDDR=1111b)

(PREMD=1)

Power Up/

Reset

(Hardware)

Not 5C6h to

WDKEY

5C6h to WDKEY

Pre-Active

State

5C6h to

WDKEY

A7Eh to

WDKEY

A7Eh to WDKEY

with ”1” to WDEN

(Reload Timer,

Clear WDFLAG,

Enable Output Pin)

Active State

(Waiting for

5C6h)

Not A7Eh or 5C6h

to WDKEY

Not 5C6h or A7Eh

to WDKEY

Output Pin Asserted

WDFLAG Set

WD INT Triggered

Timeout!

Output Pin Asserted

WDFLAG Set

WD INT Triggered

Timeout

State

(Watchdog

Disabled)

(Output Pin

Disconnected)

5C6h to

WDKEY

A7Eh to

WDKEY

(Register

Reload)

Service

State

(Waiting for

A7Eh)

5C6h to

WDKEY

Timeout!

WDFLAG Set

WD INT Triggered

Output Pin Asserted

WD INT Triggered

to WDKEY

Output Pin Asserted

WDFLAG Set

Not A7Eh or 5C6h

Figure 3−25. Watchdog Operation State Diagram

As shown in Figure 3−25, the watchdog is disabled before it enters the active state. Even though disabled,

the WD interrupt (WD_TINT) may be triggered periodically although the watchdog output pin (x_WTOUT) will

not be asserted. The interrupt may be utilized to:

•

Indicate that watchdog is not in active state

•

Allow the watchdog timer to act as a general-purpose time counter if the watchdog functionality is not

needed.

3.2.5.7

Watchdog Register Write Protection

Once the watchdog is enabled, writes to registers WDTIM, WDPRD, and WDTCR will have no effect. Writes

to the WDFLAG, WDEN, and PREMD bits in register WDTSCR will have no effect. However, writing an

incorrect key (not 5C6h or A7Eh) to WDKEY will result in an immediate time-out.

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