MEGA128CAN Datasheet, PDF (237/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

Overload Frame
Message Objects
Operating Modes
Disabled
Tx Data & Remote Frame
4250E–CAN–12/04
AT90CAN128
An overload frame is sent by setting an overload request (OVRQ). After the next recep-
tion, 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 119. Overload Frame
Instructions
Setting OVRQ bit
Resetting OVRQ bit
OVRQ bit
OVFG bit
RXCAN
TXCAN
Ident "A" Cmd
Message Data "A"
CRC A Interframe Overload Frame
Overload Frame
Ident "B"
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 pri-
ority 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
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).
Table 95. MOb Configuration
MOb Configuration Reply Valid RTR Tag Operating Mode
0
0
x
x
Disabled
x
0
Tx Data Frame
0
1
x
1
Tx Remote Frame
x
0
Rx Data Frame
1
0
0
Rx Remote Frame
1
1
Rx Remote Frame then,
Tx Data Frame (reply)
1
1
x
x
Frame Buffer Receive Mode
In this mode, the MOb is “free”.
1. Several fields must be initialized before sending:
– Identifier tag (IDT)
– Identifier extension (IDE)
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