TSS461C
17
Rev. D (22 Feb 01)
8. Diagnosis System
The purpose of the diagnosis system is to detect any short or open circuits on either the DATA or DATA lines
and to permit, if it is possible, to carry the communications on the non-defective line.
The diagnosis system is based on the assumption that three separate line receivers are connected to the VAN bus (c.f.
Figure 3. ):
One of the line receivers is connected in differential mode, sensing both DATA and DATA signals, and is connected
to the RxD0 input.
The other two line receivers are operating in single wire mode and are sensing only one of the two VAN bus signals:
the line receiver sensing DATA is connected to RxD1,
the line receiver sensing DATA is connected to RxD2.
The diagnosis system analyses and compares the data sent over both VAN lines. So, the diagnosis system executes a
digital filtering and transition analyses. In order to perform its investigation, three internal signals are generated, RI
(
Return to Idle)
, SDC (
Synchronous Diagnosis Clock)
and TIP (
Transmission In Progress
).
One of four operating modes can be chosen to manage the results of the diagnosis system.
8.1. Diagnosis States
If the diagnosis system finds a failure on either of the VAN bus signals, it changes from nominal to degraded mode,
and connects the line receiver not coupled to the failing signal to the reception logic.
When the diagnosis system finds that the failing signal is working again, it returns to nominal mode and re-connects
the differential line receiver to the reception logic.
A major error occurs when both the VAN bus signals are failed.
NONIMAL
MAJOR
ERROR
DEGRATED
DATA
DEGRATED
DATA
- Failure during the frame.
- Default of transitions on the valid input between 2 consecutive SDC rising edges.
- Protocol fault
- In specified selection mode, every RI pulse when an EOF is detected or through an active SDC.
- In automatic selection mode and SDC active, no failure sampled by 2 consecutive SDC rising edges.
- General reset
Figure 17. Diagnosis States