8XC196LX 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

 

 

64µS

1

 

 

128µS

 

 

 

 

 

 

 

 

 

 

or

0

 

 

 

0

 

 

 

 

NB for IFR with CRC

NB for IFR without CRC

 

 

A5220-01

Figure 8-7. Huntzicker Symbol Definition for the Normalization Bit

8.4.1.4Start 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

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Intel 8XC196Jx, 8XC196Lx, 8XC196Kx, 87C196CA user manual 64µS 128µS NB for IFR with CRC NB for IFR without CRC