Intel 87C196CA, Supplement To User’S Manual

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8-13
J1850 COMMUNICATIONS CONTROLLER
Figure 8-10. IFR Type 2 Message Frame
8.4.2.3 IFR Messaging Type 3: Multiple Bytes, Single Responder
IFR messaging type 3 (Figure 8-11) is ideal for requesting large amounts of information from a
single source in your system. You can compile up to 12 bytes of data from a remote node on a
single request. In our example, for the same amount of CPU overhead as IFR type 1 messaging
exhausted (4.96 ms), you can gather up to twelve times as much information.
Figure 8-11. IFR Type 3 Message Frame
8.5 TRANSMITTING AND RECEIVING MESSAGES
The J1850 controller can transmit and receive messages in either standard or IFR form.
8.5.1 Transmitting Messages
To transmit a standard message, prepare the message in register RAM and then write it to the
J1850 transmit (J_TX) register (Figure 8-12) one byte at a time.
A5227-01
0-1 Byte
CRC
E
O
D
S
O
F
E
O
F
I
F
S
The number of data bytes to be transferred is unspecified if 0EH is written to J_CMD3:0.
Each D
X
block in the IFR data field represents a byte of data from a different remote node.
1 Byte
CRC
E
O
D
N
B 1-3 Bytes
Header
1-11 Bytes
Data
†
IFR Data Field
††
In-frame Response (IFR) Frame
††
†
D
31
. . . . . . . . . .
D
1
D
0
A5228-01
0-1 Byte
CRC
E
O
D
S
O
F
E
O
F
I
F
S
The number of data bytes to be transferred is unspecified if 0EH is written to J_CMD3:0.
1-12 Bytes
IFR Data
1 Byte
CRC
E
O
D
N
B 1-3 Bytes
Header
1-11 Bytes
Data
†
In-frame Response (IFR) Frame
†