DS80C390_00 Datasheet, PDF (130/155 Pages) Dallas Semiconductor – High-Speed Microcontroller User’s Guide Supplement

DS80C390 High-Speed Microcontroller User’s Guide Supplement
CAN Message Center y Format Register (CnMyF)
MOVX
Address¹
7
6
5
4
3
2
1
0
xxxxy6h DTBYC3 DTBYC2 DTBYC1 DTBYC0 T/ R
EX/ ST MEME MDME
DTBYC3-0
Bits 7-4
T/ R
Bit 3
EX/ ST
Bit 2
MEME
Bit 1
MDME
Bit 0
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.
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.
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.
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.
Media Identification Mask Enable. The MDME bit enables (MEME = 1) or
disables (MEME = 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.
130 of 155