2.19.4 Message Data Registers (CANMDL, CANMDH)
Mailbox Layout
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Eight bytes of the mailbox are used to store the data field of a CAN message. The setting of DBO (MC.10)
determines the ordering of stored data. The data is transmitted or received from the CAN bus, starting with
byte 0.
•
When DBO (MC.10) = 1, the data is stored or read starting with the least significant byte of the
CANMDL register and ending with the most significant byte of the CANMDH register.
•
When DBO (MC.10) = 0, the data is stored or read starting with the most significant byte of the
CANMDL register and ending with the least significant byte of the CANMDH register.
The registers CANMDL(
n
) and CANMDH(
n
) can be written only if mailbox
n
is configured for transmission
(CANMD[
n
] (CANMD.31-0)=0) or the mailbox is disabled (CANME[
n
] (CANME.31-0)=0). If TRS[
n
]
(TRS.31-0)=1, the registers CANMDL(
n
) and CANMDH(
n
) cannot be written, unless CDR (MC.8)=1, with
MBNR (MC.4-0) set to
n
. These settings also apply for a message object configured in reply mode (AAM
(MSGID.29)=1).
Figure 2-31. Message-Data-Low Register With DBO = 0 (CANMDL)
31
24 23
16 15
8
7
0
Byte 0
Byte 1
Byte 2
Byte 3
Figure 2-32. Message-Data-High Register With DBO = 0 (CANMDH)
31
24 23
16 15
8
7
0
Byte 4
Byte 5
Byte 6
Byte 7
Figure 2-33. Message-Data-Low Register With DBO = 1 (CANMDL)
31
24 23
16 15
8
7
0
Byte 3
Byte 2
Byte 1
Byte 0
Figure 2-34. Message-Data-High Register With DBO = 1 (CANMDH)
31
24 23
16 15
8
7
0
Byte 7
Byte 6
Byte 5
Byte 4
Note:
The data field beyond the valid received data is modified by any message reception and is
indeterminate.
64
eCAN Registers
SPRU074F – May 2002 – Revised January 2009
