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Message Data Registers (CANMDL, CANMDH)
831
SPRUI07–March 2020
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Controller Area Network (CAN)
13.9 Message Data Registers (CANMDL, CANMDH)
Eight bytes of the mailbox are used to store the data field of a CAN message. The setting of DBO
(CANMC.10) determines the ordering of stored data. The data is transmitted or received from the CAN
bus, starting with byte 0.
• When DBO (CANMC.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 (CANMC.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 (CANMC.8)=1,
with MBNR (CANMC.4-0) set to n. These settings also apply for a message object configured in reply
mode (AAM (MSGID.29)=1).
Figure 13-40. 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 13-41. 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 13-42. 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 13-43. 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.
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