
242
7682C–AUTO–04/08
AT90CAN32/64/128
5.
Tsjw = (1 to 4) x Tscl = (SJW[1..0]+ 1) x Tscl
Notes:
1. The total number of Tscl (Time Quanta) in a bit time must be between 8 to 25.
2. PHS2[2..0] 2 is programmable to be
≤ PHS1[2..0] and ≥ 1.
19.4.4
Fault Confinement
19.4.5
Overload Frame
An overload frame is sent by setting an overload request (OVRQ). After the next reception, the
CAN channel sends an overload frame in accordance with the CAN specification. A status or
flag is set (OVRF) as long as the overload frame is sent.
Figure 19-9. Overload Frame
19.5
Message Objects
The MOb is a CAN frame descriptor. It contains all information to handle a CAN frame. This
means that a MOb has been outlined to allow to describe a CAN message like an object. The set
of MObs is the front end part of the “mailbox” where the messages to send and/or to receive are
pre-defined as well as possible to decrease the work load of the software.
The MObs are numbered from 0 up to 14 (no MOb [15]). They are independent but priority is
given to the lower one in case of multi matching. The operating modes are:
– Disabled mode
– Transmit mode
– Receive mode
– Automatic reply
– Frame buffer receive mode
19.5.1
Operating Modes
Every MOb has its own fields to control the operating mode. There is no default mode after
RESET. Before enabling the CAN peripheral, each MOb must be configured (ex: disabled mode
- CONMOB=00).
Ident "A" Cmd
Message Data "A"
CRC
Interframe
A
Ident "B"
Overload
Frame
Overload
Frame
RXCDAN
Setting OVRQ bit
OVFG bit
Resetting OVRQ bit
TXCDAN
OVRQ bit
Instructions
Table 19-1.
MOb Configuration
MOb Configuration
Reply Valid
RTR Tag
Operating Mode
0
x
Disabled
0
1
x
0
Tx Data Frame
x
1
Tx Remote Frame