UJA1069 datasheet(13/64 Pages) PHILIPS

13 / 64 page

UJA1069_2

Preliminary data sheet

Rev. 02 — 5 March 2007

13 of 64

NXP Semiconductors

UJA1069

LIN fail-safe system basis chip

Any microcontroller driven mode change is synchronized with a watchdog access by

reading the mode information and the watchdog period information from the same

switching between different software modules.

6.4.1 Watchdog start-up behavior

Following any reset event the watchdog is used to monitor the ECU start-up procedure. It

observes the behavior of the RSTN pin for any clamping condition or interrupted reset

wire. In case the watchdog is not properly served within tWD(init), another reset is forced

and the monitoring procedure is restarted. In case the watchdog is again not properly

served, the system enters Fail-safe mode (see also Figure 4, Start-up mode and Restart

mode).

6.4.2 Watchdog window behavior

Whenever the SBC enters Normal mode, the Window mode of the watchdog is activated.

This ensures that the microcontroller operates within the required speed; a too fast as well

as a too slow operation will be detected. Watchdog triggering using the Window mode is

illustrated in Figure 5.

The SBC provides 10 different period timings, scalable with a 4-factor watchdog prescaler.

The period can be changed within any valid trigger window. Whenever the watchdog is

triggered within the window time, the timer will be reset to start a new period.

The watchdog window is deﬁned to be between 50 % and 100 % of the nominal

programmed watchdog period. Any too early or too late watchdog access or wrong Mode

Fig 5.

Watchdog triggering using Window mode

mce626

trigger window

trigger

window

too early

trigger

restarts

period

50 %

trigger

via SPI

trigger

via SPI

last

trigger point

earliest possible

trigger point

latest possible

trigger point

earliest

possible

trigger

point

latest

possible

trigger

point

too early

trigger restarts period

(with different duration if

desired)

period

100 %

50 %

100 %

new period

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