ST92F124 datasheet(310/429 Pages) STMICROELECTRONICS

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J1850 Byte Level Protocol Decoder (JBLPD)

J1850 BYTE LEVEL PROTOCOL DECODER (Cont’d)

IFR2, In-Frame Response Type 2 opcode.

The In-frame Response Type 2 (IFR2) opcode is

set if the user program wants to transmit a physical

address byte (contained in the PADDR register) in

response to a message that is currently being re-

ceived.

The user program decides to set up an IFR2 upon

receiving a certain portion of the data byte string of

an incoming message. No write of the TXDATA

the PADDR register.

The JBLPD block will enable the transmission of

the IFR2 on these conditions:

– 1) The CRC check is valid (otherwise the CRCE

is set)

– 2) The received message length is valid if ena-

bled (otherwise the TRA is set)

– 3) A valid EOD minimum symbol is received (oth-

erwise the IFD may eventually get set due to

byte synchronization errors)

– 4) If NFL = 0 & Received Byte Count for this

frame <=11 (otherwise TRA is set)

– 5) If not presently executing an MSG, IFR3, op-

code (otherwise TRA is set, and TDUF will get

set because the transmit state machine will be

expecting more data, so the inverted CRC will

be appended to this frame)

– 6) If not presently executing an IFR1, IFR2, or

IFR3+CRC opcodes, otherwise TRA is set (but

no TDUF)

– 7) If not presently receiving an IFR portion of a

frame, otherwise TRA is set.

The IFR byte is then attempted according to the

procedure described in section “Transmitting a

type 2 IFR”. Note that if an IFR opcode is written, a

queued MSG or MSG+CRC is overridden by the

IFR2.

IFR3, In-Frame Response Type 3 opcode.

The In-Frame Response Type 3 (IFR3) opcode is

set if the user program wants to initiate to transmit

or continue to transmit a string of data bytes in re-

sponse to a message that is currently being re-

ceived.

The IFR3 uses the contents of the TXDATA regis-

ter for data. The user program decides to set up an

IFR3 upon receiving a certain portion of the data

byte string of an incoming message. A previous

write of the TXDATA register should have oc-

curred.

The JBLPD block will enable the transmission of

the first byte of an IFR3 string on these conditions:

– 1) The CRC check is valid (otherwise the CRCE

is set)

– 2) The received message length is valid if ena-

bled (otherwise the TRA is set)

– 3) A valid EOD minimum symbol is received (oth-

erwise the IFD may eventually get set due to

byte synchronization errors)

– 4) If NFL = 0 & Received Byte Count for this

frame <=9 (otherwise TRA is set and inverted

CRC is transmitted due to TDUF)

– 5) If not presently executing an MSG opcode

(otherwise TRA is set, and TDUF will get set be-

cause the transmit state machine will be expect-

ing more data and the inverted CRC will be

appended to this frame)

– 6) If not presently executing an IFR1, IFR2, or

IFR3+CRC opcode, otherwise TRA is set (but

no TDUF)

– 7) If not presently receiving an IFR portion of a

frame, otherwise TRA is set.

The IFR3 byte string is then attempted according

to the procedure described in section “Transmit-

ting a type 3 IFR”. Note that if an IFR3 opcode is

written, a queued MSG or MSG+CRC is overrid-

den by the IFR3.

The next byte(s) in the IFR3 data string shall also

be written with the IFR3 opcode except for the last

byte in the string which shall be written with the

IFR3+CRC opcode. Each IFR3 data byte trans-

mission is accomplished with a TXDATA/TXOP

write sequence. The succeeding IFR3 transmit re-

quests will be enabled on conditions 4 and 5 listed

above.

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