Datasheet

• The sum of the measured delay from CAN_TX to CAN_RX and the configured transceiver delay
compensation offset FBTP.TDCO has to be less than 6 bit times in the data phase.
• The sum of the measured delay from CAN_TX to CAN_RX and the configured transceiver delay
compensation offset FBTP.TDCO has to be less or equal to 127 mtq. In case this sum exceeds 127
mtq, the maximum value of 127 mtq is used for transceiver delay compensation.
• The data phase ends at the sample point of the CRC delimiter, that stops checking of receive bits at
the SSPs.
Transmitter Delay Compensation Measurement
If transmitter delay compensation is enabled by programming DBTP.TDC = ‘1’, the measurement is
started within each transmitted CAN FD frame at the falling edge of bit FDF to bit res. The measurement
is stopped when this edge is seen at the receive input CAN_TX of the transmitter. The resolution of this
measurement is one mtq.
Figure 39-2. Transceiver delay measurement
Delay
+
Start
Stop
Delay Counter
Delay Compensation Offset
SSP Position
CAN_TX
CAN_RX
GCLK_CAN
TDCR.TDCO
data phase
data phasearbitration phase
arbitration phase
Transmitter Delay
FDF
res
BRS ESI DLC
To avoid that a dominant glitch inside the received FDF bit ends the delay compensation measurement
before the falling edge of the received res bit, resulting in a too early SSP position, the use of a
transmitter delay compensation filter window can be enabled by programming TDCR.TDCF. This defines
a minimum value for the SSP position. Dominant edges of CAN_RX, that would result in an earlier SSP
position are ignored for transmitter delay measurement. The measurement is stopped when the SSP
position is at least TDCR.TDCF AND CAN _RX is low.
39.6.2.5 Restricted Operation Mode
In Restricted Operation Mode the node is able to receive data and remote frames and to give
acknowledge to valid frames, but it does not send data frames, remote frames, active error frames, or
overload frames. In case of an error condition or overload condition, it does not send dominant bits,
instead it waits for the occurrence of bus idle condition to resynchronize itself to the CAN communication.
The error counters (ECR.REC, ECR.TEC) are frozen while Error Logging (ECR.CEL) is still incremented.
The CPU can set the CAN into Restricted Operation mode by setting bit CCCR.ASM. The bit can only be
set by the CPU when both CCCR.CCE and CCCR.INIT are set to ‘1’. The bit can be reset by the CPU at
any time.
Restricted Operation Mode is automatically entered when the Tx Handler was not able to read data from
the Message RAM in time. To leave Restricted Operation Mode, the CPU has to reset CCCR.ASM.
The Restricted Operation Mode can be used in applications that adapt themselves to different CAN bit
rates. In this case the application tests different bit rates and leaves the Restricted Operation Mode after it
has received a valid frame.
SAM D5x/E5x Family Data Sheet
CAN - Control Area Network
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1210