Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 125)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
125 of 158
CnMID0 masks programmed to 1 will force the state of the corresponding Data
Byte bit and CAN Media Byte Arbitration Registers 1 and 0 to match before
considering the incoming message a match. Programming either Media ID Mask
Register to 00h effectively disables the Media ID test for that byte. As such the
CnMID1, CnMID0 masks act as a don’t care following a system Reset.
CAN Media Arbitration Register 0 (CnMA0)
MOVX
Address 1
7 6 5 4 3 2 1 0
xxxx01h
CAN Media Arbitration Register 1 (CnMA1)
MOVX
Address 1
7 6 5 4 3 2 1 0
xxxx03h
CAN Media Arbitration Register 1-0. These registers function as the arbitration
field when performing the Media Identification test. If MDME=0, the Media
Identification test will not be performed and the contents of these registers is
ignored. If MDME=1, the CAN module will perform an additional qualifying test
on Data Bytes 0 and 1 of the incoming message, as mentioned in the description of
the CAN Media ID Mask Registers. This register can only be modified during a
software initialization (SWINT=1).
CAN Bus Timing Register 0 (CnBT0)
MOVX
Address 1
7 6 5 4 3 2 1 0
xxxx04h SJW1 SJW0 BPR5 BPR4 BPR3 BPR2 BPR1 BPR0
SJW1, SJW0
Bits 7-6 CAN Synchronization Jump Width Select. These bits specify the maximum
number of time quanta (t
qu
) cycles that a bit may be lengthened or shortened in
one resynchronization to compensate for Phase Errors detected by the CAN
controller when receiving data. These bits can only be modified during a software
initialization (SWINT=1).
SJW1 SJW0 Synchronization Jump Width
(Number in parenthesis is SJW value used in bit timing calculations)
0 0 1 t
qu
(1)
0 1 2 t
qu
(2)
1 0 3 t
qu
(3)
1 1 4 t
qu
(4)
BPR5 - BPR0
Bits 5-0 CAN Baud Rate Prescaler. The sixty four states defined by the binary
combinations of the BPR5 - BPR0 bits determine the value of the prescaler,
which in turn defines the cycle time associated with one time quanta. These bits