Table 16-18. Master Control Register (CANMC) Field Descriptions (continued)
Bit
Field
Value
Description
12
CCR
Change-configuration request. This bit is EALLOW protected.
1
The CPU requests write access to the configuration register CANBTC and the acceptance mask
registers (CANGAM, LAM[0], and LAM[3]) of the SCC. After setting this bit, the CPU must wait until
the CCE flag of CANES register is at 1 before proceeding to configure the CANBTC register.
The CCR bit will also be set upon a bus-off condition, if the ABO bit is not set. The BO condition
can be exited by clearing this bit (after 128 * 11 consecutive recessive bits on the bus).
0
The CPU requests normal operation. This can be done only after the configuration register
CANBTC was set to the allowed values. It also exits the bus-off state after the obligatory bus-off
recovery sequence.
11
PDR
Power down mode request. This bit is automatically cleared by the eCAN module upon wakeup
from low-power mode. This bit is EALLOW protected.
1
The local power-down mode is requested.
0
The local power-down mode is not requested (normal operation).
Note:
If an application sets the TRS
n
bit for a mailbox and then immediately sets the PDR bit, the
CAN module goes into LPM without transmitting the data frame. This is because it takes about 80
CPU cycles for the data to be transferred from the mailbox RAM to the transmit buffer. Therefore,
the application has to ensure that any pending transmission has been completed before writing to
the PDR bit. The TA
n
bit could be polled to ensure completion of transmission.
10
DBO
Data byte order. This bit selects the byte order of the message data field. This bit is EALLOW
protected.
1
The data is received or transmitted least significant byte first.
0
The data is received or transmitted most significant byte first.
9
WUBA
Wake up on bus activity. This bit is EALLOW protected.
1
The module leaves the power-down mode after detecting any bus activity.
0
The module leaves the power-down mode only after writing a 0 to the PDR bit.
8
CDR
Change data field request. This bit allows fast data message update.
1
The CPU requests write access to the data field of the mailbox specified by the MBNR.4:0 field
(CANMC.4-0). The CPU must clear the CDR bit after accessing the mailbox. The module does not
transmit that mailbox content while 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.
Note:
Once the TRS bit is set for a mailbox and then data is changed in the mailbox using the CDR
bit, the CAN module fails to transmit the new data and transmits the old data instead. To avoid this,
reset transmission in that mailbox using the TRR
n
bit and set the TRS
n
bit again. The new data is
then transmitted.
0
The CPU requests normal operation.
7
ABO
Auto bus on. This bit is EALLOW protected.
1
After the bus-off state, the module goes back automatically into bus-on state after 128 * 11
recessive bits have been monitored.
0
The bus-off state may only be exited after 128 * 11 consecutive recessive bits on the bus and after
having cleared the CCR bit.
6
STM
Self test mode. This bit is EALLOW protected.
1
The module is in self-test mode. In this mode, the CAN module generates its own acknowledge
(ACK) signal, thus enabling operation without a bus connected to the module. The message is not
sent, but read back and stored in the appropriate mailbox. The MSGID of the received frame is not
stored in the MBR in STM.
Note:
In STM, if no MBX has been configured to receive a transmitted frame, then that frame will
be stored in MBX0, even if MBX0 has not been configured for receive operations. If LAMs are
configured such that some mailboxes can receive and store data frames, then a data frame that
does not satisfy the acceptance mask filtering criterion for any receive mailbox will be lost.
0
The module is in normal mode.
Controller Area Network (CAN)
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
1033
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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