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AP29000

Connecting C166 and C500 Microcontroller to CAN

Ways of handling the SAE 81C90/91 and the CAN Module on the C167CR / C515C

Application Note 63 V 1.0, 2004-02

• To transmit a Remote Frame, make sure that you have configured a message

object "n" (e.g. MO 2) that handles Remote Frames (RTR = 1) and that carries the

right identifier and "0" in the DLC. Like the Data Frame, the Remote Frame is

transmitted by setting the bit that corresponds to message object n in the registers

TRSR1 (messages 0 - 7) or TRSR2 (messages 8 - 15), respectively. Several bits

may be set simultaneously which results in the transmission of all

selected messages starting with the one with the highest message index.

• Please note that the corresponding Data Frame is not stored into this message

object n from which the Remote Frame was sent. Another message object

configured to handle Data Frames (RTR=0) is needed.

A possibility to avoid this:

• Configure a message object "n" that handles Remote Frames (RTR = 1) and that

carries the right identifier and "0" in the DLC.

• Transmit the Remote Frame.

• Wait until bit TC in the MOD register is set on the successful transmission of the

frame.

• Now change bit RTR in the descriptor bytes to zero and adjust the DLC.

• When now the corresponding Data Frame arrives, it will be stored in this message

object (as long as there's no other message object with RTR=0, the same identifier,

and a higher message object priority).

You have to make sure, though, that the reprogramming of the RTR bit is done before

the corresponding Data Frame is transmitted. Be also aware of the fact that the

requested Data Frame is not necessarily the frame that directly follows the transmitted

Remote Frame.

6.5.3 Evaluation of a received Message with the SAE 81C90/91

• If the SAE 81C90/91 receives a Remote Frame with an identifier that matches with

the identifier of a message object configured to handle Remote Frames (RTR=1),

then the DLC, the data bytes and the identifier remain unchanged. The Remote

Frame is automatically answered with the corresponding Data Frame.

• If the SAE 81C90/91 receives a Data Frame with an identifier that matches with the

identifier of a message object configured to handle Data Frames (RTR=0), then the

data bytes in the Data Field are copied into the data bytes of this message object.

The DLC is updated while The RTR bit and the identifier remain unchanged. The

device sets the corresponding receive-ready bit in the RRx register and bit RI in the

interrupt service routine then first has to read INT to determine the reason for the

interrupt.

Infineon C166 Series User Manual

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