33889 datasheet(34/60 Pages) FREESCALE

34 / 60 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33889

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

In application, with CAN communication, a recovery

condition is detected after 4 acknowledge bits are sent by the

MC33889B.

MC33889D:

When detection is complete, the counter is decremented

by sampling the dominant pulse (recovery pulse) on S-H (S-

L), and incremented (up to 4) by sampling the recessive pulse

(detection pulses) on S-H (S-L). It is necessary to get 4

consecutive dominant samples (recovery pulse) to get to

zero. When reaching zero, the failure is recovered.

In application with real CAN communication, a recovery

condition will not be detected by a single acknowledge bit

send by MC33889D, but requires a complete CAN message

(at least 4 dominant bits) send in dual wire mode, without

reception of any bit in single wire mode.

Tx permanent dominant detection:

In addition to the previous list, the MC33889 detects a

permanent low state at the TX input which results in a

permanent dominant bus state. If TX is low for more than

0.75-4ms, the bus output driver is disabled. This avoids

blocking communication between other nodes of the network.

TXD is reported via the SPI (RCR register bit D1:

TXFAILURE). Tx permanent dominant recovery is done with

TX recessive for more than typ 32us.

Rx pin behavior while CAN interface is in TermVbat.

The MC33889D is able to signal bus activity on Rx while

the CAN interface is in TermVbat and the SBC in normal or

standby mode. When the bus is driven into a dominant state

by another sending node, each dominant state is reported at

Rx by a low level, after a delay of TWAKE.

The bus state report is done through the CAN interface

wake up comparator on CANL and CANH, and thus operates

also in case of bus failure. This is illustrated in the following

figure.

33889 Datasheet(PDF) 34 Page - Freescale Semiconductor, Inc