Specifications
CAN Control Registers
10-24
Bit 8 CDR. Change Data Field Request
The CDR bit is applicable for mailboxes 2 and 3 only
and
in the following situa-
tion: 1) either (or both) of these mailboxes are configured for transmission and
2) the corresponding AAM bit is set.
0 The CPU requests normal operation.
1 The CPU requests write access to the data field of the mailbox in
MBNR (located also in MCR). The CDR bit must be cleared by the
CPU after accessing the mailbox. The CAN module does not transmit
the mailbox if the CDR is set. This is checked by the state machine
before and after it reads the data from the mailbox to store it in the
transmit buffer.
Bit 7 ABO. Auto Bus On
0
The bus-off state may only be left after 128 × 11 consecutive
recessive bits on the bus and after having reset the CCR bit.
1 After the bus-off state, the module goes back to the bus-on state after
128 × 11 consecutive recessive bits.
Bit 6 STM. Self Test Mode
0 The module is in normal mode.
1 The module is in Self Test mode. In this mode, the CAN module
generates its own ACK signal. Thus, it enables operation without a
bus connected to the module. The message is not sent but read back
and stored in the appropriate mailbox. The remote frame handling
with Auto Answer mode set is
not
implemented in STM.
Bits 5–2 Reserved.
Bits 1–0 MBNR. Mailbox Number (for CDR bit assertion)
The CPU requests a write access to the data field for the mailbox hav-
ing this number and configured for Remote Frame Handling. These
are mailboxes 2 (10) or 3 (11), but not 0, 1, 4 or 5.
10.4.5 Bit Configuration Registers (BCR
n
)
The bit configuration registers (BCR1 and BCR2) are used to configure the
CAN node with the appropriate network timing parameters. These registers
must be programmed before using the CAN module and are writeable only in
configuration mode. The CCR bit must be set to put the CAN module in config-
uration mode.
Note:
To avoid unpredictable behavior, BCR1, 2 should never be programmed with
values not allowed by the CAN protocol specification.