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8XC196L X SUPPLEMENT
(J_CFG.7) and considers whether the IFR message response has a CRC byte appended. Figure
8-7 depicts the SAE preferred, active-level state bit format timing for the NB.
1
0
NB for IFR without CRC
Figure 8-7. Huntzicker Symbol Definition for the Normalization Bit
8.4.1.4
Start and End Message Frame Symbols
Five symbols are used to mark the start and end of a message frame and to allow the J1850 bus
to properly recognize the interruption of a message transmission or reception. Figure 8-8 illus-
trates the formats and their respective timing.
The following is a description of each symbol:
•
start of frame (SOF) — this symbol signals the start of a message frame. This is an active-
level state symbol only and appears once per frame.
•
end of data (EOD) — this symbol signals the end of the data transmission. This is a passive-
level state symbol only. It appears twice in IFR messaging: at the end of the initial request
data field and at the end of the IFR data field.
•
end of frame (EOF) — this symbol signals the end of a message frame and returns the bus
to an idle state. This is a passive-level state symbol only. It appears once per frame.
•
in-frame separation (IFS) — the timing of this symbol allows for proper synchronization of
multiple nodes during back-to-back transmissions. Nodes contending for the bus must
comply with one of two conditions before transmitting:
— wait for the IFS minimum timing to expire
— wait for a rising edge on the bus after the EOF minimum timing has expired
•
break (BRK) — this symbol signals an interruption during a bus transmission. At the point
of termination, all nodes are reset. This is an active-level state symbol.
8-10
64µS
or
128µS
1
0
NB for IFR with CRC
A5220-01
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