Datasheet

The resolution of this measurement is one mtq.
Figure 49-2. T
ransmitter Delay Measurement
arbitration phase
data phase
Delay Counter
Start Stop
BRS DLCFDF
E
S
I
res
Transmitter
data phase
arbitration phase
Delay Compensation Offset
SSP Position
Delay
Delay
MCAN_TDCR.TDCO
CANTX
CANRX
CAN core clock
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 to early SSP position, the use of a transmitter delay compensation
filter window can be enabled by programming MCAN_TDCR.TDCF
.
This defines a minimum value for the SSP position. Dominant edges on CANRX, 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 MCAN_TDCR.TDCF AND CANRX is low.
49.5.1.5 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 are not incremented. The processor
can set the MCAN into Restricted Operation mode by setting bit MCAN_CCCR.ASM. The bit can only be set by the
processor when both MCAN_CCCR.CCE and MCAN_CCCR.INIT are set to ‘1’. The bit can be reset by the processor
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 processor has to reset MCAN_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.
Note: The Restricted Operation Mode must not be combined with the Loop Back mode (internal or external).
49.5.1.6 Bus Monitoring Mode
The MCAN is set in Bus Monitoring mode by setting MCAN_CCCR.MON. In Bus Monitoring mode (see ISO11898-1,
10.12 Bus monitoring), the MCAN is able to receive valid data frames and valid remote frames, but cannot start a
transmission. In this mode, it sends only recessive bits on the CAN bus. If the MCAN is required to send a dominant
bit (ACK bit, overload flag, active error flag), the bit is rerouted internally so that the MCAN monitors this dominant bit,
although the CAN bus may remain in recessive state. In Bus Monitoring mode, the Tx Buf
fer Request Pending
register (MCAN_TXBRP) is held in reset state.
The Bus Monitoring mode can be used to analyze the traffic on a CAN bus without affecting it by the transmission of
dominant bits. The figure below shows the connection of signals CANTX and CANRX to the MCAN in Bus Monitoring
mode.
SAM E70/S70/V70/V71 Family
Controller Area Network (MCAN)
©
2019 Microchip Technology Inc.
Datasheet
DS60001527D-page 1409