16.4.5 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 16-9. Overload Frame
Instructions
Setting OVRQ bit
Resetting OVRQ bit
OVRQ bit
OVFG bit
RXCDAN
TXCDAN
Ident “A” Cmd Message Data “A”
CRC
A
Interframe Overload Frame
Overload Frame
Ident “B”
16.5 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 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
16.5.1 Number of MObs
This device has 6 MObs, they are numbered from 0 up to 5 (i=5).
16.5.2 Operating Modes
There is no default mode after RESET.
Every MOb has its own fields to control the operating mode. Before enabling the CAN peripheral, each MOb must be
configured (ex: disabled mode - CONMOB=00).
Table 16-1. MOb Configuration
MOb Configuration
Reply Valid
RTR Tag
Operating Mode
0
0
x
x
x
x
0
1
x
x
0
1
0
Disabled
Tx Data Frame
0
1
Tx Remote Frame
Rx Data Frame
1
0
1
Rx Remote Frame
1
x
Rx Remote Frame then, Tx Data Frame (reply)
Frame Buffer Receive Mode
1
16.5.2.1 Disabled
In this mode, the MOb is “free”.
ATmega16/32/64/M1/C1 [DATASHEET]
149
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
