UJA1069 datasheet(10/64 Pages) PHILIPS

10 / 64 page

UJA1069_2

Preliminary data sheet

Rev. 02 — 5 March 2007

10 of 64

NXP Semiconductors

UJA1069

LIN fail-safe system basis chip

Interrupts from SBC to the host microcontroller are also monitored. A system reset is

performed if the host microcontroller does not respond within tRSTN(INT). Entering Normal

mode does not activate the LIN transceiver automatically. The LIN Mode Control (LMC) bit

must be used to activate the LIN medium if required, allowing local cyclic wake-up

scenarios to be implemented without affecting the LIN-bus.

6.2.5 Standby mode

In Standby mode the system is set into a state with reduced current consumption. The

watchdog will, however, continue to monitor the microcontroller (Time-out mode) since it is

powered via pin V1.

In the event that the host microcontroller can provide a low-power mode with reduced

current consumption in its Standby mode or Stop mode, the watchdog can be switched off

entirely in Standby mode of the SBC. The SBC monitors the microcontroller supply current

to ensure that there is no unobserved phase with disabled watchdog and running

microcontroller. The watchdog will remain active until the supply current drops below

IthL(V1). Below this current limit the watchdog is disabled.

Should the current increase to IthH(V1), e.g. as result of a microcontroller wake-up from

application speciﬁc hardware, the watchdog will start operating again with the previously

used time-out period. If needed, an interrupt can be issued when the watchdog restarts. If

the watchdog is not triggered correctly, a system reset will occur and the SBC will enter

Start-up mode.

If Standby mode is entered from Normal mode with the selected watchdog OFF option,

the watchdog will use the maximum time-out as deﬁned for Standby mode until the supply

current drops below the current detection threshold; the watchdog is now OFF. If the

current increases again, the watchdog is immediately activated, again using the maximum

watchdog time-out period. If the watchdog OFF option is selected during Standby mode,

the last used watchdog period will deﬁne the time for the supply current to fall below the

current detection threshold. This allows the user to align the current supervisor function to

the application needs.

Generally, the microcontroller can be activated from Standby mode via a system reset or

via an interrupt without reset. This allows implementation of differentiated start-up

behavior from Standby mode, depending on the application needs:

• If the watchdog is still running during Standby mode, the watchdog can be used for

cyclic wake-up behavior of the system. A dedicated Watchdog Time-out Interrupt

Enable (WTIE) bit enables the microcontroller to decide whether to receive an

interrupt or a hardware reset upon overﬂow. The interrupt option will be cleared in

hardware automatically with each watchdog overﬂow to ensure that a failing main

routine is detected while the interrupt service still operates. So the application

software must set the interrupt behavior each time before a standby cycle is entered.

• Any wake-up via the LIN-bus together with a local wake-up event will force a system

reset event or an interrupt to the microcontroller. So it is possible to exit Standby mode

without any system reset if required.

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