PXN20RM Datasheet, PDF (898/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Controller Area Network (FlexCAN)
Table 29-7. CANx_MCR Field Descriptions (continued)
Field
Description
BCC
Backwards Compatibility Configuration. Provided to support backwards compatibility with previous FlexCAN
versions. When this bit is negated, the following configuration is applied:
• For MCUs supporting individual Rx ID masking, this feature is disabled. Instead of individual ID masking per
MB, FlexCAN uses its previous masking scheme with CANx_RXGMASK, CANx_RX14MASK, and
CANx_RX15MASK.
• The reception queue feature is disabled. On receiving a message, if the first MB with a matching ID that is
found is still occupied by a previous unread message, FlexCAN does not look for another matching MB. It
overrides this MB with the new message and sets the CODE field to 0b0110 (overrun).
This bit is cleared on reset, allowing legacy software to work without modification.
0 Individual Rx masking and queue feature are disabled.
1 Individual Rx masking and queue feature are enabled.
LPRIO_EN
Local Priority Enable. Provided for backwards compatibility reasons. It controls whether the local priority feature
is enabled or not. It is used to extend the ID used during the arbitration process. With this extended ID concept,
the arbitration process is done based on the full 32-bit word, but the actual transmitted ID still has 11 bits for
standard frames and 29 bits for extended frames.
0 Local priority disabled.
1 Local priority enabled.
AEN
Abort Enable. Provided for backwards compatibility reasons. When set, it enables the Tx abort feature. This
feature guarantees a safe procedure for aborting a pending transmission, so that no frame is sent in the CAN
bus without notification.
0 Abort disabled.
1 Abort enabled.
IDAM
ID Acceptance Mode. Identifies the format of the elements of the Rx FIFO filter table. All elements of the table
are configured at the same time by this field (they are all the same format).
IDAM Format
Explanation
00
A One full ID (standard or extended) per filter element.
01
B Two full standard IDs or two partial 14-bit extended IDs per filter element.
10
C Four partial 8-bit IDs (standard or extended) per filter element.
11
D All frames rejected.
MAXMB
Maximum Number Of Message Buffers. This 6-bit field defines the maximum number of message buffers of the
FlexCAN module. The reset value (0x0F) is equivalent to a 16 MB configuration. This field should be changed
only while the module is in freeze mode.
Maximum MBs in use = MAXMB + 1
Note: MAXMB must be programmed with a value smaller or equal to the number of available message buffers,
otherwise FlexCAN can transmit and receive wrong messages.
29.3.4.2 Control Register (CANx_CTRL)
This register is defined for specific FlexCAN control features related to the CAN bus, such as bit-rate,
programmable sampling point within an Rx bit, loop back mode, listen only mode, bus off recovery
behavior, and interrupt enabling (bus-off, error, warning). It also determines the division factor for the
clock prescaler. Most of the fields in this register should only be changed while the module is disabled or
29-14
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor