mc33889 Freescale Semiconductor, Inc, mc33889 Datasheet - Page 33

• Manufacturer Part Number: mc33889
• Description: System Basis Chip With Low Speed Fault Tolerant Can Interface
• Manufacturer: Freescale Semiconductor, Inc

Open wire detection, MC33889B and D:
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.
wire detection is performed only when the device
receives a message and not when it send message.
Analog Integrated Circuit Device Data
Freescale Semiconductor
Failure detection:
The device will detect a difference in toggling counts
(No open wire, or open wire recovery)
CANH
CANL
S-L
Diff
S-H
-3.2V
Rec
Sampling dominant level
= > no failure or “recovery pulse”
Figure 13. CAN Normal Signal Communication and CAN Open Wire
Dom
CANH
CANL
Figure 14. Open Wire Detection Principle
1us
Sampling point
Rec
Diff
The open
S-H
S-L
Dom Rec
1us
1us
(count = 4)
Sampling recessive level
= > open wire “detection pulse”
Sampling
Sampling
L-open
in count is reduced and the device detects the open wire
recovery.
MC33889B:
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
L-counter +/-
S-L
Diff
S-H
-3.2V
Open wire recovery:
When the open wire failure has recovered, the difference
When detection is complete, the counter is no longer
Rec
(CAN H open wire)
CANH counter
(count = 0)
recover
Dom
Sampling point
FUNCTIONAL DEVICE OPERATION
Rec
OPERATIONAL MODES
33889
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