33889 datasheet(33/60 Pages) FREESCALE

33 / 60 page

Analog Integrated Circuit Device Data

Freescale Semiconductor

33889

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

Figure 13. CAN Normal Signal Communication and CAN Open Wire

Figure 14. Open Wire Detection Principle

Open wire detection, MC33889B and D:

Failure detection:

The device will detect a difference in toggling counts

between the differential receiver and one of the single ended

receivers. Every time a difference in count is detected a

counter is incremented. When the counter reaches 4, the

device detects and reports an open wire condition.

The open

wire detection is performed only when the device

receives a message and not when it send message.

Open wire recovery:

When the open wire failure has recovered, the difference

in count is reduced and the device detects the open wire

recovery.

MC33889B:

When detection is complete, the counter is no longer

incremented. It can only be decremented by sampling of the

dominant level on the S-H (S-L) (recovery pulse). When it

reaches zero, the failure has recovered.

CANH

CANL

Diff

S-L

S-H

-3.2V

Rec

Dom

Rec

Sampling point

CANH

CANL

Diff

S-L

S-H

-3.2V

Rec

Dom

Rec

Sampling point

Sampling recessive level

= > open wire “detection pulse”

1us

(No open wire, or open wire recovery)

(CAN H open wire)

Sampling dominant level

= > no failure or “recovery pulse”

Diff

CANH

CANL

S-H

1us

Sampling

Dom Rec

S-L

1us

Sampling

CANH counter

L-open

L-counter +/-

(count = 4)

recover

(count = 0)

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