Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 132)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
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CAN Message Center y Format Register (CnMyF)
MOVX
Address 1 7 6 5 4 3 2 1 0
xxxxy6h DTBYC3 DTBYC2 DTBYC1 DTBYC0 T/ R EX/ ST MEME MDME
DTBYC3-0
Bits 7-4 Data Byte Count. These bits indicate the number of bytes within the data field of the
message. When performing a transmit, software sets the DTBYC bits to establish the
number of bytes that are to be transmitted. When receiving a message, the DTBYC bits
indicate the (binary) number of bytes of data in the incoming message; i.e., 0000b = 0
data bytes and 1000b = 8 data bytes.
T/ R
Bit 3 Transmit/Receive Select. This bit is programmed by the application software to indicate
if the message is to be transmitted (
T/ R = 1) or received ( T/ R = 0). This bit can only be
modified when MSRDY = 0.
This bit does not exist for Message Center 15 and will always return 0 when read from
Message Center 15.
EX/ST
Bit 2 Extended or Standard Identifier. This bit determines whether the respective message
is to utilize the extended 29-bit Identification format (EX/ ST = 1) or the standard 11-bit
Identification format (EX/ST = 0). Message centers programmed for one format will
only receive/send extended messages in that format and will ignore the alternate format.
This bit can only be modified when MSRDY = 0.
MEME
Bit 1 Message Identification Mask Enable. The MEME bit enables (MEME = 1) or disables
(MEME = 0) the use of the Message Identification Masking process, associated with the
testing of the Identification field in the incoming message. This bit can only be modified
when MSRDY = 0.
0 = The mask registers are ignored when evaluating the identification bits of the
incoming message, and the identification bits of the incoming message and the
message center arbitration bits must match exactly to allow receipt of the incoming
message. This is equivalent to programming the mask with all zeros. An exact match
is also required before a remote data request is allowed.
1 = The mask registers are enabled, comparing only those bits message identification and
arbitration bits which correspond to a 1 in the mask register. When this bit is set and
the ID of an incoming message matches the masked ID of a message center, the ID
of the incoming message overwrites the message center ID.
MDME
Bit 0 Media Identification Mask Enable. The MDME bit enables (MDME = 1) or disables
(MDME = 0) the use of the first two bytes of the data field as a message qualifier. This
bit can only be modified when MSRDY = 0.
0 = The first two bytes of the data field are ignored and not compared.
1 = The first two data bytes are masked by the respective Media Mask ID Register and
then compared with the Media Arbitration Register Zero and One bytes. Only those
bits in the first two data bytes and the arbitration registers corresponding to a 1 in the
mask register are compared. When MDME=1 the test is also performed before a
remote request of data from a remote node is accepted.