Intel 8XC196Lx Manuale Utente
8-17
J1850 COMMUNICATIONS CONTROLLER
J_CMD
Address:
Reset State:
1F51H
00H
The J1850 command (J_CMD) register determines the messaging type, specifies the number of bytes
to be transmitted in the next message frame, and updates the status of the message transmission in
progress. This byte register can be directly addressed through
to be transmitted in the next message frame, and updates the status of the message transmission in
progress. This byte register can be directly addressed through
windowing
. You must write to this
register prior to transmitting every message.
7
0
AUTO
IFR
IGNORE
ABORT
MSG3
MSG2
MSG1
MSG0
Bit
Number
Bit
Mnemonic
Function
7
AUTO
Automatic Transmit Retry
This bit, when arbitration is lost on the first byte of your message, prompts
the transmitter to automatically retry until the byte is successfully
transmitted. Automatic retry applies only to the first byte.
the transmitter to automatically retry until the byte is successfully
transmitted. Automatic retry applies only to the first byte.
0 = normal operation
1 = enable automatic retry
1 = enable automatic retry
6
IFR
In-frame Response Indicator
This bit signals that a normalization bit (NB) is to be sent after an end-of-
data symbol is detected on the bus and that the subsequent byte written to
the J1850 transmitter (J_TX) register is an in-frame response (IFR).
data symbol is detected on the bus and that the subsequent byte written to
the J1850 transmitter (J_TX) register is an in-frame response (IFR).
0 = standard messaging
1 = next byte written to J_TX is an IFR
1 = next byte written to J_TX is an IFR
5
IGNORE
Ignore Incoming Message
This bit instructs the bus to ignore the incoming message until an EOF
symbol is detected. The bit is cleared after an EOF symbol is detected.
symbol is detected. The bit is cleared after an EOF symbol is detected.
0 = normal operation
1 = ignore incoming message
1 = ignore incoming message
4
ABORT
Abort Transmission
This bit aborts any transmission in progress and flushes the transmit buffer
(JTX_BUF). To prevent another node from mistakenly assuming that the
last byte was a CRC byte, two extra ‘1’s are appended.
(JTX_BUF). To prevent another node from mistakenly assuming that the
last byte was a CRC byte, two extra ‘1’s are appended.
0 = normal operation
1 = abort transmission in progress
1 = abort transmission in progress
3:0
MSG3:0
Message
These four bits specify the number of bytes to be transmitted in the next
message frame. This number includes the header, but not the CRC byte. In
normal messaging, the maximum number of bytes you can transmit in a
message frame is eleven.
message frame. This number includes the header, but not the CRC byte. In
normal messaging, the maximum number of bytes you can transmit in a
message frame is eleven.
MSG3:0
Operation
Purpose
FH
Termination byte
Terminate block transmission
EH
Block transmission Transmit unspecified number of bytes
DH
Reserved
—
CH
Reserved
—
B:0H
Normal messaging Transmit specified number of bytes
Figure 8-16. J1850 Command (J_CMD) Register