HC705V8GRSSLASHD datasheet(135/172 Pages) NXP

135 / 172 page

SECTION 15: MESSAGE DATA LINK CONTROLLER

Page 124

MC68HC705V8 Specification Rev. 2.1

15.5.4.4

Valid EOD Symbol

If the passive to active transition beginning the next data bit or symbol occurs between

and

d, the current symbol would be considered a valid EOD symbol. See Figure 15-12(4).

15.5.4.5

Valid EOF & IFS Symbol

If the passive to active transition beginning the SOF symbol of the next message occurs

between

a and b, 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 between

c and

d, the current symbol will be considered a valid EOF symbol followed by a valid IFS symbol.

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. See Figure 15-13(1&2).

15.5.4.6

Idle Bus

If the passive to active transition beginning the SOF symbol of the next message does not

occur before

d, the bus is considered to be idle, and any node wishing to transmit a

message may do so immediately.

(2) Valid EOF+

IFS Symbol

280

µs

580

µs

(1) Valid EOF

Symbol

Figure 15-13:

J1850 VPW EOF and IFS Symbols

Active

Passive

Active

Passive

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC705V8GRS/D Datasheet(PDF) 135 Page - NXP Semiconductors

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