Functional Description
MPC5200B Users Guide, Rev. 1
Freescale Semiconductor 20-23
Figure 20-7. J1850 VPW EOF and IFS Symbols
Valid EOF & IFS Symbol
In Figure 20-7(1), if the passive to active transition beginning the SOF symbol of the next message occurs between Trv4(Min) and
Trv4(Max), the current symbol will be considered a valid EOF symbol.
If the passive to active transition beginning the SOF symbol of the next message occurs after Trv5(Min), the current symbol will be
considered a valid EOF symbol followed by a valid IFS symbol. See Figure 20-7(2). All nodes must wait until a valid IFS symbol
time has expired before beginning transmission. However, due to variations in clock frequencies and bus loading, some nodes may
recognize a valid IFS symbol before others, and immediately begin transmitting. Therefore, anytime a node waiting to transmit
detects a passive to active transition once a valid EOF has been detected, it should immediately begin transmission, initiating the
arbitration process.
Idle Bus
If the passive to active transition beginning the SOF symbol of the next message does not occur before Ttv5(Min), the bus is
considered to be idle, and any node wishing to transmit a message may do so immediately.
(2) Valid EOF+
IFS Symbol
280µs
300µs
Trv4(Min) Trv4(Max)
(1) Valid EOF
Symbol
Active
Passive
Active
Passive Trv5(Min)