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M451
May. 4, 2018
Page
868
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1006
Rev.2.08
M4
51
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started.
Configuring a Receive Object
6.20.7.9
The Table 6-37 shows how a Receive Object should be initialized.
MsgV
a
l
A
rb
D
a
ta
Mas
k
E
oB
D
ir
N
e
wD
a
t
MsgLst
R
x
IE
TxIE
Int
P
n
d
R
m
tE
n
TxR
qst
1
appl.
appl.
appl.
1
0
0
0
appl.
0
0
0
0
Table 6-37 Initialization of a Receive Object
The Arbitration Registers values (ID28-0 (CAN_IFn_ARB1/2) and Xtd bit (CAN_IFn_ARB2[14])) are
provided 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. Then ID17 - ID0 can be
disregarded. When a Data Frame with an 11-bit Identifier is received, ID17 -
ID0 will be set to ‘0’.
If the RxIE bit (CAN_IFn_MCON[10]) is set, the IntPnd bit (CAN_IFn_MCON[13]) will be set when a
received Data Frame is accepted and stored in the Message Object.
The Data Length Code (DLC3-0 (CAN_IFn_MCON[3:0])) is provided 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 unspecified values.
The Mask Registers (Msk28-0, UMask, MXtd and MDir bits) may be used (UMask
(CAN_IFn_MCON[12]) = ’1’) to allow groups of Data Frames with similar identifiers to be accepted.
The Dir bit (CAN_IFn_ARB2[13]) should not be masked in typical applications.
Handling Received Messages
6.20.7.10
The application software may read a received message any time through the IFn Interface registers.
The data consistency is guaranteed by the Message Handler state machine.
Typically, the software will write first 0x007F to the Command Mask Register and then the number of
the Message Object to the Command Request Register. This combination will transfer the whole
received message from the Message RAM into the Message Buffer Register. Additionally, the bits
NewDat (CAN_IFn_MCON[15]) and IntPnd (CAN_IFn_MCON[13]) are cleared in the Message RAM
(not in the Message Buffer).
If the Message Object uses masks for acceptance filtering, the arbitration bits show which of the
matching messages have been received.
The actual value of NewDat shows whether a new message has been received since the last time this
Message Object was read. The actual value of MsgLst (CAN_IFn_MCON[14]) shows whether more
than one message has been received since the last time this Message Object was read. MsgLst will
not be automatically reset.
By means of a Remote Frame, the software may request another CAN node to provide new data for a
receive object. Setting the TxRqst bit (CAN_IFn_MCON[8]) of a receive object will cause the
transmission of a Remote Frame with the receive object’s identifier. 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.
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