Intel 87C196CA, 8XC196Jx, 8XC196Lx Transmitting and Receiving Messages, Transmitting Messages

J1850 COMMUNICATIONS CONTROLLER

In-frame Response (IFR) Frame							IFR Data Field††
S	1-3 Bytes	1-11 Bytes	1 Byte	E	N	D	D	D
O				O
F	Header	Data†	CRC	D	B	0	1	31

0-1 Byte

CRC

E

O D

EI

OF

FS

†

The number of data bytes to be transferred is unspecified if 0EH is written to J_CMD3:0.

†† Each DX block in the IFR data field represents a byte of data from a different remote node.

A5227-01

Figure 8-10. IFR Type 2 Message Frame

8.4.2.3IFR 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.

In-frame Response (IFR) Frame
S	1-3 Bytes	1-11 Bytes		1 Byte	E	N	1-12 Bytes	0-1 Byte	E	E	I
O					O				O	O	F
				CRC			IFR Data	CRC
F	Header	Data	†		D	B			D	F	S

†The number of data bytes to be transferred is unspecified if 0EH is written to J_CMD3:0.

A5228-01

Figure 8-11. IFR Type 3 Message Frame

8.5TRANSMITTING AND RECEIVING MESSAGES

The J1850 controller can transmit and receive messages in either standard or IFR form.

8.5.1Transmitting 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.

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