3 ifx message control registers, 4 ifx data a and data b registers, 4 message object in the message memory – Bosch TTCAN User Manual
Page 24: Message object in the message memory, Example for bit timing at low baudrate, Chapter 3.3.4)
User’s Manual
BOSCH
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Revision 1.6
TTCAN
11.11.02
manual_about.fm
3.3.3.3 IFx Message Control Registers
3.3.3.4 IFx Data A and Data B Registers
The data bytes of CAN messages are stored in the IFx registers in the following order:
In a CAN Data Frame, Data(0) is the first, Data(7) is the last byte to be transmitted or received.
In CAN’s serial bit stream, the MSB of each byte will be transmitted first.
3.3.4 Message Object in the Message Memory
There are 32 Message Objects in the Message RAM. To avoid conflicts between CPU access
to the Message RAM and CAN message reception and transmission, the CPU cannot directly
access the Message Objects, these accesses are handled via the IFx Interface Registers.
Figure 7 gives an overview of the two structure of a Message Object.
Figure 7: Structure of a Message Object in the Message Memory
MsgVal
Message Valid
one
The Message Object is configured and should be considered by the Mes-
sage Handler.
zero
The Message Object is ignored by the Message Handler.
Note :
The CPU must reset the MsgVal bit of all unused Messages Objects during the initialization
before it resets bit Init in the CAN Control Register. This bit must also be reset before the iden-
tifier Id28-0, the control bits Xtd, Dir, or the Data Length Code DLC3-0 are modified, or if the
Messages Object is no longer required.
UMask
Use Acceptance Mask
one
Use Mask (Msk28-0, MXtd, and MDir) for acceptance filtering
zero
Mask ignored.
Note :
If the UMask bit is set to
one
, the Message Object’s mask bits have to be programmed during
initialization of the Message Object before MsgVal is set to
one
.
IF1 Message Control Register
(addresses 0x1D & 0x1C)
15
14
13
12
11
10
9
8
7
6
5
4 3 2 1 0
NewDat MsgLst IntPnd UMask TxIE RxIE RmtEn TxRqst EoB
MSC2-0
DLC3-0
IF2 Message Control Register
(addresses 0x4D & 0x4C)
NewDat MsgLst IntPnd UMask TxIE RxIE RmtEn TxRqst EoB
MSC2-0
DLC3-0
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
rw
15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
IF1 Message Data A1 (addresses 0x1F & 0x1E)
Data(1)
Data(0)
IF1 Message Data A2 (addresses 0x21 & 0x20)
Data(3)
Data(2)
IF1 Message Data B1 (addresses 0x23 & 0x22)
Data(5)
Data(4)
IF1 Message Data B2 (addresses 0x25 & 0x24)
Data(7)
Data(6)
IF2 Message Data A1 (addresses 0x4F & 0x4E)
Data(1)
Data(0)
IF2 Message Data A2 (addresses 0x51 & 0x50)
Data(3)
Data(2)
IF2 Message Data B1 (addresses 0x53 & 0x52)
Data(5)
Data(4)
IF2 Message Data B2 (addresses 0x55 & 0x54)
Data(7)
Data(6)
rw
rw
Message Object
UMask
Msk28-0
MXtd
MDir
EoB
MSC2-0 NewDat MsgLst RxIE
TxIE IntPnd RmtEn TxRqst
MsgVal
ID28-0
Xtd
Dir
DLC3-0 Data 0
Data 1 Data 2 Data 3 Data 4 Data 5 Data 6 Data 7