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33902 Datasheet, PDF (16/31 Pages) Freescale Semiconductor, Inc – High Speed CAN Interface with Embedded 5.0 V Supply
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FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
The flag is cleared by leaving the Normal mode or by a
P_SPI reading.
Using the P_SPI, it is possible to get detailed failure
information.
WAKE Pin - Local Wake-up (WU)
From the Standby, Go To Sleep or Sleep mode, this flag is
set if a transition on the WAKE pin is detected. This wake-up
is reported on the ERR pin by a low level in Standby mode,
as well as in Sleep mode if VIO is present.
The wake-up flag is cleared by leaving the Normal mode
or by P_SPI reading.
Wake-up Source
Wake-up source is reported on the ERR pin by entering
Normal mode, before 4 TX pulses. The ERR pin is low to
indicate a local wake-up, and high to indicate CAN wake-up.
Local Failure
This flag is a logic «OR» of the following failures: TXD
dominant clamping, RXD recessive clamping, TXD-to-RXD
short-circuit and VDD low condition. This flag is reported in
Listen Only on the ERR pin coming from Normal mode.
Using the P_SPI, it is possible to get detailed failure
information.
BUS Failure
The BUS failure flag is set if the CAN transceiver detects
a bus line short-circuit condition to VSUP, VDD, or GND,
during five consecutive dominant-recessive cycles on the
TXD pin. In addition, this flag reports a bus dominant
clamping condition. In Normal mode, the bus failure flag is
available on the ERR pin.
VDD low
VDD low flag is set in Normal and Listen Only mode when
VDD is below the VDD low threshold. After a time longer than
tVDD-CANOFF, the CAN is disabled and after a time longer than
tVDDOFF, the VDD regulator is disabled to avoid a battery
discharge.
If the CRANK bit is set high, the VDD regulator and CAN
will not be disabled if VSUP is below VSUV. When VSUP is
above VSUV, the CRANK bit has no effect.
VDD low flag is reported in Normal and Listen Only mode,
so the user can differentiate between local and bus failures
by changing modes and observing ERR staying low.
In case of a double failure (local and bus failure) at the
same time, the results will be the same: ERR low in Normal
and in Listen Only mode. However, this is unlikely to occur.
This flag is cleared when entering low power, or when VDD
is above VDD low threshold, plus the P_SPI reading.
The VDD regulator is re enabled as soon as VSUP rises
above VSUP low, or by a mode change (refer to the crank
pulse illustration).
The CAN is re-enabled as soon as VDD is above VDD low
threshold. (refer to crank pulse illustration).
ERR Pin
The ERR pin reports various information depending upon
the device state, the device state transition, and event on the
TXD pin.
Table 6 shows the diagnostic flag availability when the
device is controlled in a static manner.
Table 6. “Static” Diagnostic Flags
Flag
BATFAIL
CANWU or Local WU
Wake-up source
BUS Failure
Local Failure
VDD low
Evaluation mode
Accessibility
Listen-Only mode (coming from Standby, Go-to-Sleep, Sleep)
Standby, Go-to-Sleep, Sleep (provided VIO is present)
Normal mode (Before the fourth dominant to recessive edge on the
TXD pin)
Normal mode (After the fourth dominant to recessive edge on the
TXD pin)
Listen Only mode (coming from Normal mode)
Normal mode (After the fourth dominant to recessive edge on the
TXD pin) and Listen Only mode (coming from Normal mode)
By RXD low, when coming from Sleep or Standby into Normal or
Listen Only modes.
Clearing Diagnostic
Leaving Normal mode
Leaving Normal mode or by setting the BATFAIL
Leaving Normal mode, or by setting BATFAIL flag.
Re-entering Normal mode
Entering Normal mode or TXD high while RXD low.
VDD > VDD low threshold
RXD goes from low to high, to signal the device is ready
and has exited low power modes (TLP-NP parameter).
33902
16
Analog Integrated Circuit Device Data
Freescale Semiconductor
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