RM0319 datasheet(204/368 Pages) STMICROELECTRONICS

204 / 368 page

Controller area network ports (CAN)

RM0319

204/368

Doc ID 022640 Rev 3

15.4.13

Configuring a receive object

Table 61 shows how a receive object should be initialized.

Table 61.

Initialization of a receive object

The Arbitration registers (ID28-0 and Xtd bit) are given by the application. They define the

identifier and type of accepted received messages. If an 11-bit Identifier (“Standard Frame”)

is used, it is programmed to ID28 - ID18. ID17 - ID0 can then be disregarded. When a data

frame with an 11-bit Identifier is received, ID17 - ID0 will be set to ‘0’.

If the RxIE bit is set, the IntPnd bit will be set when a received data frame is accepted and

stored in the message object.

The data length code (DLC3-0) is given by the application. When the message handler

stores a data frame in the message object, it will store the received data length code and

eight data bytes. If the data length code is less than 8, the remaining bytes of the message

object will be overwritten by non specified values.

The Mask registers (Msk28-0, UMask, MXtd, and MDir bits) may be used (UMask=’1’) to

allow groups of data frames with similar identifiers to be accepted. For details, see

Reception of data frame. The Dir bit should not be masked in typical applications.

15.4.14

Handling received messages

The CPU may read a received message any time via the IFx Interface registers, the data

consistency is guaranteed by the message handler state machine.

Typically, the CPU will write first 0x007F to the Command Mask register and then the

number of the message object to the Command Request register. That combination will

transfer the whole received message from the message RAM into the message buffer

the message buffer).

If the message object uses masks for acceptance filtering, the arbitration bits show which of

the matching messages has been received.

The actual value of NewDat shows whether a new message has been received since last

time this message object was read. The actual value of MsgLst shows whether more than

one message has been received since last time this message object was read. MsgLst will

not be automatically reset.

By means of a remote frame, the CPU may request another CAN node to provide new data

for a receive object. Setting the TxRqst bit of a receive object will cause the transmission of

a remote frame with the identifier of the receive object. this remote frame triggers the other

CAN node to start the transmission of the matching data frame. if the matching data frame is

received before the remote frame could be transmitted, the TxRqst bit is automatically reset.

MsgVal

Arb

Data

Mask

EoB

Dir

NewDat

MsgLst

RxIE

TxIE

IntPnd

RmtEn

TxRqst

appl.

RM0319 датащи(PDF) 204 Page - STMicroelectronics

RM0319 датащи(HTML) 204 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL