L4969UR-E datasheet(21/46 Pages) STMICROELECTRONICS

21 / 46 page

L4969UR-E, L4969URD-E

Functional description

Doc ID 022587 Rev 2

21/46

After detecting a dominant level on either CANH or CANL for longer than the wakeup filter

time (twuCAN), RX goes low for one tOSC cycle. This is repeated cyclically every twuREP until

CANx returns to a recessive state or CANx is considered as shorted to a dominant value.

Note, that the duration of the extended cycle twuREP equals twuCAN when the oscillator is in

1 MHz mode (Standby3, RXOnly and Normal mode, see Table 15).

If the device uses the low power oscillator (250 KHz) in either Sleep2 or Standby2

twuREP = 4.2 x twuCAN.

3.4

Oscillator

A low power oscillator provides an internal clock, that can be calibrated in a range from

-16% to +16% via the RCADJ register using the µC-XTAL as a reference.

In the operating modes Sleep2 and Standby2 (Watchdog / timer active) the output frequency

is ~250 kHz (1/ tOSCslow), if the Watchdog function is not requested, the internal Oscillator is

switched off.

In the operating modes Normal, RXonly and Standby3 the oscillator is running at ~1 MHz

(1/ tOSC).

3.5

Watchdog

A triple function programmable watchdog is integrated to perform the following tasks:

●

Wakeup watchdog:

When in sleep or standby mode the watchdog can generate a wakeup condition after a

programmable period of time ranging from 80 ms up to 45 minutes

●

Startup watchdog:

Upon V1 power-up or microcontroller failure during SPI supervision a reset pulse is

generated periodically every 320 ms for 2.5 ms until activity of the microcontroller is

detected (SPI sequence) or no acknowledge is received within 7 cycles (2.2 sec). In

this condition the device is forced into Sleep mode until a Wakeup is detected and a

startup cycle is reinitialized.

●

Window watchdog:

After passing the startup sequence, this watchdog request an acknowledge by the

microcontroller via the SPI within a programmable timing frame, ranging from 2.5 ...

5 ms up to 20 ... 40 ms. Upon a missing or misplaced acknowledge the Startup

Watchdog is initialized.

3.6

Reset

3.6.1

Power-on reset

Upon Power-on (VS > 3.5 V), the internal reset forces the device into a predefined power-On

state (see Section 3.1: General features):

Standby #3: V1 on V2 off V3 off,CAN-Standby mode, ID-Filter disabled, startup watchdog

active.

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